JEADV
DOI: 10.1111/jdv.12833
REVIEW ARTICLE
A new vision of actinic keratosis beyond visible clinical lesions J. Malvehy* Melanoma Skin Unit, University Hospital Clinic of Barcelona, Barcelona, Spain *Correspondence: J. Malvehy. E-mail: [email protected]
Abstract In actinic keratosis (AK), clinical and subclinical lesions coexist across large areas of sun-exposed skin resulting in field cancerization. The lesions are part of a disease continuum which can progress into invasive squamous cell carcinoma (SCC). Conventional biopsy sampling together with histopathological analysis of the excised tissue is still the gold standard for differentially diagnosing AK from invasive SCC and identifying the characteristic pathophysiological features of these lesions. Given that biopsy sampling is invasive and not suited to the investigation of disease across large fields of skin, several imaging technologies have been applied to non-invasively investigate AK. Widely available imaging technologies such as cross-polarized light, fluorescence and dermoscopy can assist the dermatologist in diagnosing AK and in identifying different types of AK lesions. Modern imaging technologies such as reflectance confocal microscopy (RCM) and high-definition optical coherence tomography (HD-OCT) provide high-resolution images of the skin. These techniques can be used to image the histological changes that characterize AK and so can be used to diagnose the disease and its severity. They can also identify the presence of subclinical lesions and non-invasively monitor the effects of AK treatments on both subclinical and clinical lesions over time. Both RCM and HD-OCT have revealed a new vision of AK by visualizing in detail the cellular and histological changes that characterize both clinical and subclinical lesions, and confirming that the disease affects the entire sun-exposed field. As a consequence of these findings, the target for the treatment of AK now needs to be the detection and clearance of all clinical and subclinical lesions across the entire sunexposed field. Received: 4 September 2014; Accepted: 6 October 2014
Conflict of interest Consultant for the following companies: Meda Pharma, Leo Pharma, Almirall, ISDIN, Roche Posay, Pierre Farma, Mavig, 3Gen, Bristol Meyers Squibb, Amgen, Roche Pharma
Funding source This supplement was funded by Meda Pharma GmbH & Co. KG.
Introduction In actinic keratosis (AK), the entire area of sun-exposed skin is affected by disease resulting in field cancerization. The concept of field cancerization was first introduced by Slaughter et al.1 in 1953 to describe histologically abnormal tissue surrounding primary oral squamous cell carcinoma (SCC) and to explain the development of multiple primary tumours and locally recurrent cancer within the field. This concept was extended by Braakhuis et al.2 who in 2003 proposed that clusters of genetically altered stem cell clonal units develop into individual and then contiguous fields of pre-neoplastic cells. In AK, the visible clinical lesions are the initial manifestation of a multi-step carcinogenesis process or disease continuum that can progress from initial subclinical keratinocyte dysplasia into invasive SCC. Field cancerization
JEADV 2015, 29 (Suppl. 1), 3–8
develops since ultraviolet light causes neoplastic changes across the entire sun-exposed field of skin. Within the cancerous field, all stages of AK may coexist including individual UV-damaged keratinocytes, subclinical (invisible, non-palpable) lesions, early clinical lesions, late clinical lesions, and in some patients, invasive SCC.3 According to Braakhuis et al.2 the consequence of this pathophysiology is that the ‘treatment of epithelial cancers should not only be focused on the tumour but also on the field from which it developed’. In terms of AK, this means that all lesions across an entire sun-exposed field need to be targeted and eliminated to provide long-term disease remission and to prevent disease recurrence. The purpose of this article is to discuss how modern imaging technologies, in particular reflectance confocal microscopy
© 2014 European Academy of Dermatology and Venereology
Malvehy
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(RCM) and high-definition optical coherence tomography (HD-OCT), have been used to generate a new vision of AK. These imaging techniques visualize both clinical and subclinical lesions and so allow the full extent of a patient’s disease burden to be evaluated. They also allow a patient’s response to fielddirected treatment and the ability of the treatment to clear clinical and subclinical lesions to be assessed. High-resolution imaging is currently mainly used in a research setting, though may be increasingly used in a clinical setting in the future.
Histopathology of skin biopsies An initial vision and understanding of the pathophysiology of AK were largely based on histopathological analysis of skin biopsies. Such investigations revealed characteristic histopathological changes in the skin of AK patients which can be used to diagnose the disease and to assess its severity.4,5 These changes include parakeratosis and hyperkeratosis in the stratum corneum; abnormal architecture, irregular acanthosis and cellular pleomorphisms in the stratum granulosum and spinosum; crowding of keratinocytes and cellular pleomorphism in the stratum basale; and solar elastosis and increased vascularity in the dermis.6 In addition, the dermo-epidermal junction may appear irregular as a result of small round buds which extend into the upper papillary dermis from the basal cell layer.4 Histopathology of skin biopsies from AK patients has also shown that AK lesions and SCC are indistinguishable at a cellular level. Both AK lesions and SCC contain atypical keratinocytes with loss of polarity, nuclear polymorphism and disordered maturation.4 Investigations have also shown that these two types of lesions contain similar genetic mutations, e.g. in p53 and bcl-2 genes.7,8 As a consequence, AK is now considered to be in situ SCC.3 Skin biopsies together with histopathological analysis are recommended if invasive SCC is suspected so that the patient may receive appropriate treatment.9
Non-invasive technologies are required to further understand the pathophysiology of AK given the limitations of biopsy analysis of skin tissue. In particular, the results from biopsies are only applicable to the area from which the biopsy was taken and they cannot be used to visualize pathophysiological changes across an entire affected field of skin. In addition, repeat biopsies cannot be taken from the same area to evaluate changes over time, e.g. in response to an AK treatment. Furthermore, AK lesions can sometimes occur in areas where biopsies are not feasible, and biopsies involve patient discomfort, time and expense. New imaging techniques may also assist in the accurate noninvasive diagnosis of AK and SCC. Diagnosing lesions on the basis of clinical inspection alone can lead to a high rate of misdiagnosis. For example, the results from one study showed that 36% of lesions diagnosed clinically as AKs were actually invasive SCC when classified with histology.10 A second study identified a lower rate of clinical misdiagnosis: 9% of lesions identified clinically as AK were shown by analysis of biopsies to have other classifications such as SCC or basal cell carcinoma.11 Clinical inspection of an AK patient also does not identify subclinical lesions.
Cross-polarized light and fluorescence Cross-polarized light and fluorescence are relatively simple imaging techniques which can be used to detect subclinical AK lesions which are not normally visible.12 Cross-polarized light can be used to enhance the imaging of vasculature, pigmentation and structures below the skin surface and involves the use of specific filters on the source of illumination.12 Fluorescence involves the topical application of methyl-aminolevulinic acid, which induces porphyrin formation in the skin if clinical or subclinical disease is present.12 Of these techniques, cross-polarized light is easy to use, whereas fluorescence diagnosis is more time-con-
Figure 1 Vision of actinic keratosis with standard light compared with multimodal light and fluorescence. In the image with standard light (left), most of the patient’s actinic keratoses are not visible. With green ultraviolet light (right), actinic keratoses can be seen as white scales.
JEADV 2015, 29 (Suppl. 1), 3–8
© 2014 European Academy of Dermatology and Venereology
New imaging techniques for AK
Figure 2 Typical ‘strawberry pattern’ identified by dermoscopy of skin from a patient with early actinic keratosis. Dermoscopy reveals a characteristic red pseudonetwork outlined by erythema interrupted by hair follicles (magnification of 20x).
suming but more sensitive for detecting subclinical lesions.12 The images generated by these techniques reveal that AK affects the entire area of sun-exposed skin with many more lesions than are visible to the naked eye (Fig. 1). In addition, the clinical AK lesions themselves may be much larger than can be seen with normal light.
Dermoscopy Dermoscopy can be used as a real-time, non-invasive imaging technique to assist in the diagnosis of AK with a high level of
5
concordance between diagnoses made using this technique and with histopathology.13 Dermoscopy allows the uncovering of features such as vascular patterns which cannot be seen with the naked eye.14 Four criteria for the diagnosis of facial AK with dermoscopy have been established.14 These include erythema with a marked pink-to-red pseudonetwork surrounding hair follicles; white-to-yellow surface scale; fine, linear-wavy vessels surrounding hair follicles; and hair follicle openings filled with yellowish keratotic plugs and/or surrounded by a white halo. These features lead to a typical ‘strawberry pattern’ in 95% of patients (Fig. 2). The features most consistently found with dermoscopy of AK lesions are the erythematous pseudonetwork and follicular openings.13 A recent study showed that the dermoscopic patterns associated with AK, intraepidermal carcinoma and invasive SCC are significantly different and this may help in the early differential diagnosis of in situ or invasive lesions so that they may be appropriately treated.15 A red pseudonetwork was significantly associated with AK, whereas dotted/glomerular vessels, diffuse yellow opaque scales and microerosions were significantly more prevalent in intraepidermal carcinoma. Typical dermoscopic features of invasive SCC were hairpin vessels, linear irregular vessels, targetoid hair follicles, white structureless areas, a central mass of keratin and ulceration.15
Reflectance confocal microscopy Reflectance confocal microscopy uses infrared laser light to noninvasively examine skin in vivo in real time without the use of fluorescence, dyes or stains. The contrast observed in the RCM image correlates to naturally occurring variations in the refractive index of organelles and micro-structures in the skin. RCM
Figure 3 Comparison of images of reflectance confocal microscopy (Vivascope 1500) of subclinical actinic keratosis (left) and normal skin (right) of the same site in a patient before and after treatment. The image shows a field of 1.5 mm of the spinous layer of the epidermis. On the left side, the changes associated with subclinical actinic keratosis are atypical honeycomb with irregularity in the size and shape of corneocytes. In contrast the confocal image on the right shows a typical honeycomb.
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© 2014 European Academy of Dermatology and Venereology
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images allow the visualization of cellular and subcellular structures in the skin, similar to the detail seen in histology sections, but without the need for an invasive biopsy procedure.16 RCM has been used in the diagnosis of several dermatological conditions including melanoma and basal cell carcinoma.16 Reflectance confocal microscopy enables the histological changes that characterize AK to be imaged and so can be used in the diagnosis of this disease.6,17 RCM also enables the initial changes in epidermal morphology and cellular atypia to be visualized before the disease becomes clinically apparent and is therefore useful for the evaluation of AK field cancerization and the detection of subclinical AK (Fig. 3).18 The main RCM features of clinical AK lesions are: disruption and parakeratosis in the stratum corneum; pleomorphism and architectural disruption in the stratum granulosum and stratum spinosum with loss of the normal honeycomb pattern; and solar elastosis and increased vascularity or blood vessel dilatation in the superficial dermis.6,16–18 Of these features, cellular pleomorphism and architectural disarray are considered the best predictors of AK.6 The principal RCM features of subclinical AK lesions are pleomorphism and architectural disruption in the stratum spinosum (Fig. 3), but not in the stratum granulosum, and solar elastosis.18 Reflectance confocal microscopy can also be used in the differential diagnosis of AK and SCC, which is important since the two types of lesions require different therapeutic approaches. A study which compared RCM images of AK lesions and SCC demonstrated that SCC shows an increased frequency of abnormal RCM features compared with AK.19 The key RCM features of SCC are the presence of an atypical honeycomb pattern and round nucleated cells corresponding to atypical keratinocytes in the stratum spinosum and stratum granulosum, and round blood vessels crossing the dermal papilla. These blood vessels are
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scarcer in AK since these lesions are smaller and less developed neoplasms.19 Reflectance confocal microscopy allows the effects of AK treatments such as imiquimod or diclofenac sodium to be monitored by non-invasively examining subclinical and clinical lesions in vivo over time.18,20–22 An RCM investigation into the effects of imiquimod on actinic field cancerization demonstrated that this field-directed treatment unmasks previously invisible subclinical lesions and is able to effectively treat both clinical and subclinical lesions. Furthermore, RCM can detect any residual subclinical disease remaining after initial treatment with imiquimod and so can identify patients who may benefit from additional cycles of therapy.18 After 2 weeks of imiquimod treatment, RCM imaging of clinical and subclinical lesions revealed the presence of inflammatory cells in the dermis and epidermis, which correspond to the immunomodulatory response induced by this treatment. Four weeks after treatment with imiquimod was completed, RCM imaging demonstrated that clinical and subclinical lesions had been cleared, e.g. by revealing that the typical honeycomb pattern at the level of stratum granulosum and spinosum had been re-established.18 Similarly, RCM imaging revealed that 2 weeks of treatment with diclofenac sodium resulted in a significant decrease in scaling and in the atypical honeycomb pattern in AK patients.20 RCM has also been used to non-invasively diagnose actinic cheilitis (AK on the lip) and to visualize the response to treatment with diclofenac sodium by demonstrating the absence of cellular atypia and rearrangement of the epidermal architecture.21
High-definition optical coherence tomography Optical coherence tomography (OCT) is a non-invasive imaging technique that has been used to diagnose and monitor a variety
Figure 4 High-definition optical coherence tomography slice imaging of normal skin (top panel) and skin from a patient with actinic keratosis (lower panel) (Skintell, AGFA) (field of 1 mm in diameter). In the image of normal skin, the epidermis is regular with normal thickness and the dermo-epidermal junction is clear and has a typical shape. In contrast, in the image of the patient with actinic keratosis, the thickness of the epidermis is irregular. The stratum corneum is thickened with an increase in contrast due to keratin and the dermo-epidermal junction is flat. Epid, epidermis; DEJ, dermo-epidermal junction.
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© 2014 European Academy of Dermatology and Venereology
New imaging techniques for AK
of dermatological disorders (e.g. AK, psoriasis, contact dermatitis, cutaneous lupus erythematosus, basal cell carcinoma).23 It is based on the interference of infrared radiation and tissue samples and is used to generate real-time 2-D or 3-D cross-sectional images of biological tissues such as the skin. OCT allows noninvasive in vivo investigation of the stratum corneum, the epidermis, the dermo-epidermal junction and the upper dermis.23 The OCT technique provides real-time skin images to a depth of several millimetres depending on the tissue studied and to a resolution of a few micrometres (commonly 5–10 lm), but cannot display distinct morphological or cellular features.23 More recently, high-definition OCT (HD-OCT) has been developed to provide improved lateral and axial resolution of 3 lm, although with a reduced penetration depth of 750 lm.24,25 This resolution allows visualization of architectural changes and cellular features. With HD-OCT, both horizontal (en-face mode) and conventional vertical (slice mode) imaging can be performed. Recent studies have shown that HD-OCT enables the in vivo non-invasive diagnosis of AD, allows the grading of different types of AK lesions and the identification of subclinical lesions.25,26 In addition, the technique was shown to offer additional information in the diagnosis of AK compared with regular OCT in both the conventional slice (vertical) and in the en-face (horizontal) imaging modes.25 En-face HD-OCT imaging of AK lesions reveals similar features to RCM such as disruption of the stratum corneum; architectural disarray in the epidermis with an atypical honeycomb pattern; cellular and nuclear polymorphism in the stratum granulosum and stratum spinosum; and bright irregular bundles in the superficial dermis. In contrast, en-face HD-OCT imaging of healthy skin reveals a regular honeycomb pattern in the stratum granulosum and stratum spinosum, and shows no interruption of the stratum corneum.25 Vertical slice imaging of AK lesions reveals an irregular entrance signal, lack of distinct layering, white streaks and dots, and grey areas. These features contrast to vertical slice images of healthy skin which show distinct layering of the epidermis and dermis (Fig. 4).25 The images obtained from HD-OCT of AK lesions were found to correlate with the features identified by conventional histology. For example, the disruption of the stratum corneum detected by HD-OCT imaging correlates with the parakeratosis identified by histology, and the architectural disarray in the stratum granulosum and stratum spinosum seen in HD-OCT images correlates with the destruction of the epidermal structure observed in histology.25,26 The extent of the disruption of the honeycomb pattern in the epidermis observed by HD-OCT was shown to correlate with the severity of AK. For example, subclinical lesions are characterized by a mildly atypical honeycomb pattern in the bottom third of the epidermis, whereas clinical lesions have more extensive disruption of the honeycomb pattern.26 HD-OCT imaging of sun-damaged skin surrounding AK lesions shows features of solar elastosis and a slightly irregular honeycomb pattern.26
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Comparison of RCM and HD-OCT The respective advantages of RCM and HD-OCT mean that these techniques generate complementary information which together can provide a complete picture of the full extent and burden of a patient’s disease. The main advantage of RCM is that it provides images of greater resolution than HD-OCT (1.5 vs. 3 lm). Although both imaging technologies can be used to identify cells in the epidermis,27 the improved resolution of RCM means that both cellular and subcellular morphology can be visualized in detail.25,26 The key benefit of HD-OCT is that it provides images to a greater depth than RCM (750 vs. 250 lm) and so allows imaging of deeper layers of the skin. In addition, unlike RCM which can only image horizontal sections of skin, HD-OCT provides both horizontal and vertical images of skin and may also be used for rapid 3-D imaging.25–27
Conclusions Biopsy sampling together with histopathological analysis is not feasible for the detailed investigation of field cancerization which characterizes AK. In contrast, new imaging technologies such as RCM and HD-OCT allow non-invasive objective morphological characterization of AK field cancerization and assessment of response to field-directed treatments. Together, the results from these new imaging techniques clearly demonstrate that the disease burden of AK consists of both clinical and subclinical lesions across the entire sun-exposed field. The consequence of this pathophysiology is that the target for the treatment of AK needs to be the detection and elimination of all clinical and subclinical lesions across the entire sun-exposed field.
Acknowledgements Editorial assistance in the preparation of this manuscript was provided by David Harrison, Medscript Communications and was funded by Meda Pharma GmbH & Co. KG.
References 1 Slaughter DP, Southwick HW, Smejkal W. Field cancerization in oral stratified squamous epithelium; clinical implications of multicentric origin. Cancer 1953; 6: 963–968. 2 Braakhuis BJ, Tabor MP, Kummer JA, Leemans CR, Brakenhoff RH. A genetic explanation of Slaughter’s concept of field cancerization: evidence and clinical implications. Cancer Res 2003; 63: 1727–1730. 3 Stockfleth E, Ortonne JP, Alomar A. Actinic keratosis and field cancerisation. Eur J Dermatol 2011; 21(Suppl 1): 3–12. 4 Cockerell CJ. Pathology and pathobiology of the actinic (solar) keratosis. Br J Dermatol 2003; 149(Suppl 66): 34–36. 5 Goldberg LH, Mamelak AJ. Review of actinic keratosis. Part I: etiology, epidemiology and clinical presentation. J Drugs Dermatol 2010; 9: 1125– 1132. 6 Ulrich M, Maltusch A, Rius-Diaz F et al. Clinical applicability of in vivo reflectance confocal microscopy for the diagnosis of actinic keratoses. Dermatol Surg 2008; 34: 610–619. 7 Stanimirovic A, Cupic H, Bosnjak B, Kruslin B, Belicza M. Expression of p53, bcl-2 and growth hormone receptor in actinic keratosis, hypertrophic type. Arch Dermatol Res 2003; 295: 102–108.
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8 Hussein MR, Al-Badaiwy ZH, Guirguis MN. Analysis of p53 and bcl-2 protein expression in the non-tumorigenic, pretumorigenic, and tumorigenic keratinocytic hyperproliferative lesions. J Cutan Pathol 2004; 31: 643–651. 9 European Dermatology Forum. Guideline on actinic keratoses. Available at: http://www.euroderm.org/images/stories/guidelines/guideline_Management_Actinic_Keratoses-update2011.pdf (last accessed: September 2014). 10 Suchniak JM, Baer S, Goldberg LH. High rate of malignant transformation in hyperkeratotic actinic keratoses. J Am Acad Dermatol 1997; 37: 392–394. 11 Ehrig T, Cockerell C, Piacquadio D, Dromgoole S. Actinic keratoses and the incidence of occult squamous cell carcinoma: a clinical-histopathologic correlation. Dermatol Surg 2006; 32: 1261–1265. 12 Ortonne JP, Gupta G, Ortonne N, Duteil L, Queille C, Mallefet P. Effectiveness of cross polarized light and fluorescence diagnosis for detection of sub-clinical and clinical actinic keratosis during imiquimod treatment. Exp Dermatol 2010; 19: 641–647. 13 Huerta-Brogeras M, Olmos O, Borbujo J et al. Validation of dermoscopy as a real-time noninvasive diagnostic imaging technique for actinic keratosis. Arch Dermatol 2012; 148: 1159–1164. 14 Zalaudek I, Giacomel J, Argenziano G et al. Dermoscopy of facial nonpigmented actinic keratosis. Br J Dermatol 2006; 155: 951–956. 15 Zalaudek I, Giacomel J, Schmid K et al. Dermatoscopy of facial actinic keratosis, intraepidermal carcinoma, and invasive squamous cell carcinoma: a progression model. J Am Acad Dermatol 2012; 66: 589–597. 16 Ulrich M, Lange-Asschenfeldt S, Gonzalez S. Clinical applicability of in vivo reflectance confocal microscopy in dermatology. G Ital Dermatol Venereol 2012; 147: 171–178. 17 Horn M, Gerger A, Ahlgrimm-Siess V et al. Discrimination of actinic keratoses from normal skin with reflectance mode confocal microscopy. Dermatol Surg 2008; 34: 620–625. 18 Ulrich M, Krueger-Corcoran D, Roewert-Huber J, Sterry W, Stockfleth E, Astner S. Reflectance confocal microscopy for noninvasive monitoring of
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therapy and detection of subclinical actinic keratoses. Dermatology 2010; 220: 15–24. Rishpon A, Kim N, Scope A et al. Reflectance confocal microscopy criteria for squamous cell carcinomas and actinic keratoses. Arch Dermatol 2009; 145: 766–772. Malvehy J, Roldan-Marin R, Iglesias-Garcia P, Diaz A, Puig S. Monitoring treatment of field cancerisation with 3% diclofenac sodium 2.5% hyaluronic acid by reflectance confocal microscopy: a histologic correlation. Acta Derm Venereol 2014; doi: 10.2340/00015555-1860 [Epub ahead of print]. Ulrich M, Gonzalez S, Lange-Asschenfeldt B et al. Non-invasive diagnosis and monitoring of actinic cheilitis with reflectance confocal microscopy. J Eur Acad Dermatol Venereol 2011; 25: 276–284. Gonzalez S, Sanchez V, Gonzalez-Rodriguez A, Parrado C, Ullrich M. Confocal microscopy patterns in nonmelanoma skin cancer and clinical applications. Actas Dermosifiliogr 2014; 105: 446–458. Gambichler T, Jaedicke V, Terras S. Optical coherence tomography in dermatology: technical and clinical aspects. Arch Dermatol Res 2011; 303: 457–473. Maier T, Sattler E, Braun-Falco M, Ruzicka T, Berking C. High-definition optical coherence tomography for the in vivo detection of demodex mites. Dermatology 2012; 225: 271–276. Maier T, Braun-Falco M, Laubender RP, Ruzicka T, Berking C. Actinic keratosis in the en-face and slice imaging mode of high-definition optical coherence tomography and comparison with histology. Br J Dermatol 2013; 168: 120–128. Boone MA, Norrenberg S, Jemec GB, Del Marmol V. Imaging actinic keratosis by high-definition optical coherence tomography. Histomorphologic correlation: a pilot study. Exp Dermatol 2013; 22: 93–97. Boone M, Jemec GB, Del Marmol V. High-definition optical coherence tomography enables visualization of individual cells in healthy skin: comparison to reflectance confocal microscopy. Exp Dermatol 2012; 21: 740–744.
© 2014 European Academy of Dermatology and Venereology
DOI: 10.1111/jdv.12833
REVIEW ARTICLE
A new vision of actinic keratosis beyond visible clinical lesions J. Malvehy* Melanoma Skin Unit, University Hospital Clinic of Barcelona, Barcelona, Spain *Correspondence: J. Malvehy. E-mail: [email protected]
Abstract In actinic keratosis (AK), clinical and subclinical lesions coexist across large areas of sun-exposed skin resulting in field cancerization. The lesions are part of a disease continuum which can progress into invasive squamous cell carcinoma (SCC). Conventional biopsy sampling together with histopathological analysis of the excised tissue is still the gold standard for differentially diagnosing AK from invasive SCC and identifying the characteristic pathophysiological features of these lesions. Given that biopsy sampling is invasive and not suited to the investigation of disease across large fields of skin, several imaging technologies have been applied to non-invasively investigate AK. Widely available imaging technologies such as cross-polarized light, fluorescence and dermoscopy can assist the dermatologist in diagnosing AK and in identifying different types of AK lesions. Modern imaging technologies such as reflectance confocal microscopy (RCM) and high-definition optical coherence tomography (HD-OCT) provide high-resolution images of the skin. These techniques can be used to image the histological changes that characterize AK and so can be used to diagnose the disease and its severity. They can also identify the presence of subclinical lesions and non-invasively monitor the effects of AK treatments on both subclinical and clinical lesions over time. Both RCM and HD-OCT have revealed a new vision of AK by visualizing in detail the cellular and histological changes that characterize both clinical and subclinical lesions, and confirming that the disease affects the entire sun-exposed field. As a consequence of these findings, the target for the treatment of AK now needs to be the detection and clearance of all clinical and subclinical lesions across the entire sunexposed field. Received: 4 September 2014; Accepted: 6 October 2014
Conflict of interest Consultant for the following companies: Meda Pharma, Leo Pharma, Almirall, ISDIN, Roche Posay, Pierre Farma, Mavig, 3Gen, Bristol Meyers Squibb, Amgen, Roche Pharma
Funding source This supplement was funded by Meda Pharma GmbH & Co. KG.
Introduction In actinic keratosis (AK), the entire area of sun-exposed skin is affected by disease resulting in field cancerization. The concept of field cancerization was first introduced by Slaughter et al.1 in 1953 to describe histologically abnormal tissue surrounding primary oral squamous cell carcinoma (SCC) and to explain the development of multiple primary tumours and locally recurrent cancer within the field. This concept was extended by Braakhuis et al.2 who in 2003 proposed that clusters of genetically altered stem cell clonal units develop into individual and then contiguous fields of pre-neoplastic cells. In AK, the visible clinical lesions are the initial manifestation of a multi-step carcinogenesis process or disease continuum that can progress from initial subclinical keratinocyte dysplasia into invasive SCC. Field cancerization
JEADV 2015, 29 (Suppl. 1), 3–8
develops since ultraviolet light causes neoplastic changes across the entire sun-exposed field of skin. Within the cancerous field, all stages of AK may coexist including individual UV-damaged keratinocytes, subclinical (invisible, non-palpable) lesions, early clinical lesions, late clinical lesions, and in some patients, invasive SCC.3 According to Braakhuis et al.2 the consequence of this pathophysiology is that the ‘treatment of epithelial cancers should not only be focused on the tumour but also on the field from which it developed’. In terms of AK, this means that all lesions across an entire sun-exposed field need to be targeted and eliminated to provide long-term disease remission and to prevent disease recurrence. The purpose of this article is to discuss how modern imaging technologies, in particular reflectance confocal microscopy
© 2014 European Academy of Dermatology and Venereology
Malvehy
4
(RCM) and high-definition optical coherence tomography (HD-OCT), have been used to generate a new vision of AK. These imaging techniques visualize both clinical and subclinical lesions and so allow the full extent of a patient’s disease burden to be evaluated. They also allow a patient’s response to fielddirected treatment and the ability of the treatment to clear clinical and subclinical lesions to be assessed. High-resolution imaging is currently mainly used in a research setting, though may be increasingly used in a clinical setting in the future.
Histopathology of skin biopsies An initial vision and understanding of the pathophysiology of AK were largely based on histopathological analysis of skin biopsies. Such investigations revealed characteristic histopathological changes in the skin of AK patients which can be used to diagnose the disease and to assess its severity.4,5 These changes include parakeratosis and hyperkeratosis in the stratum corneum; abnormal architecture, irregular acanthosis and cellular pleomorphisms in the stratum granulosum and spinosum; crowding of keratinocytes and cellular pleomorphism in the stratum basale; and solar elastosis and increased vascularity in the dermis.6 In addition, the dermo-epidermal junction may appear irregular as a result of small round buds which extend into the upper papillary dermis from the basal cell layer.4 Histopathology of skin biopsies from AK patients has also shown that AK lesions and SCC are indistinguishable at a cellular level. Both AK lesions and SCC contain atypical keratinocytes with loss of polarity, nuclear polymorphism and disordered maturation.4 Investigations have also shown that these two types of lesions contain similar genetic mutations, e.g. in p53 and bcl-2 genes.7,8 As a consequence, AK is now considered to be in situ SCC.3 Skin biopsies together with histopathological analysis are recommended if invasive SCC is suspected so that the patient may receive appropriate treatment.9
Non-invasive technologies are required to further understand the pathophysiology of AK given the limitations of biopsy analysis of skin tissue. In particular, the results from biopsies are only applicable to the area from which the biopsy was taken and they cannot be used to visualize pathophysiological changes across an entire affected field of skin. In addition, repeat biopsies cannot be taken from the same area to evaluate changes over time, e.g. in response to an AK treatment. Furthermore, AK lesions can sometimes occur in areas where biopsies are not feasible, and biopsies involve patient discomfort, time and expense. New imaging techniques may also assist in the accurate noninvasive diagnosis of AK and SCC. Diagnosing lesions on the basis of clinical inspection alone can lead to a high rate of misdiagnosis. For example, the results from one study showed that 36% of lesions diagnosed clinically as AKs were actually invasive SCC when classified with histology.10 A second study identified a lower rate of clinical misdiagnosis: 9% of lesions identified clinically as AK were shown by analysis of biopsies to have other classifications such as SCC or basal cell carcinoma.11 Clinical inspection of an AK patient also does not identify subclinical lesions.
Cross-polarized light and fluorescence Cross-polarized light and fluorescence are relatively simple imaging techniques which can be used to detect subclinical AK lesions which are not normally visible.12 Cross-polarized light can be used to enhance the imaging of vasculature, pigmentation and structures below the skin surface and involves the use of specific filters on the source of illumination.12 Fluorescence involves the topical application of methyl-aminolevulinic acid, which induces porphyrin formation in the skin if clinical or subclinical disease is present.12 Of these techniques, cross-polarized light is easy to use, whereas fluorescence diagnosis is more time-con-
Figure 1 Vision of actinic keratosis with standard light compared with multimodal light and fluorescence. In the image with standard light (left), most of the patient’s actinic keratoses are not visible. With green ultraviolet light (right), actinic keratoses can be seen as white scales.
JEADV 2015, 29 (Suppl. 1), 3–8
© 2014 European Academy of Dermatology and Venereology
New imaging techniques for AK
Figure 2 Typical ‘strawberry pattern’ identified by dermoscopy of skin from a patient with early actinic keratosis. Dermoscopy reveals a characteristic red pseudonetwork outlined by erythema interrupted by hair follicles (magnification of 20x).
suming but more sensitive for detecting subclinical lesions.12 The images generated by these techniques reveal that AK affects the entire area of sun-exposed skin with many more lesions than are visible to the naked eye (Fig. 1). In addition, the clinical AK lesions themselves may be much larger than can be seen with normal light.
Dermoscopy Dermoscopy can be used as a real-time, non-invasive imaging technique to assist in the diagnosis of AK with a high level of
5
concordance between diagnoses made using this technique and with histopathology.13 Dermoscopy allows the uncovering of features such as vascular patterns which cannot be seen with the naked eye.14 Four criteria for the diagnosis of facial AK with dermoscopy have been established.14 These include erythema with a marked pink-to-red pseudonetwork surrounding hair follicles; white-to-yellow surface scale; fine, linear-wavy vessels surrounding hair follicles; and hair follicle openings filled with yellowish keratotic plugs and/or surrounded by a white halo. These features lead to a typical ‘strawberry pattern’ in 95% of patients (Fig. 2). The features most consistently found with dermoscopy of AK lesions are the erythematous pseudonetwork and follicular openings.13 A recent study showed that the dermoscopic patterns associated with AK, intraepidermal carcinoma and invasive SCC are significantly different and this may help in the early differential diagnosis of in situ or invasive lesions so that they may be appropriately treated.15 A red pseudonetwork was significantly associated with AK, whereas dotted/glomerular vessels, diffuse yellow opaque scales and microerosions were significantly more prevalent in intraepidermal carcinoma. Typical dermoscopic features of invasive SCC were hairpin vessels, linear irregular vessels, targetoid hair follicles, white structureless areas, a central mass of keratin and ulceration.15
Reflectance confocal microscopy Reflectance confocal microscopy uses infrared laser light to noninvasively examine skin in vivo in real time without the use of fluorescence, dyes or stains. The contrast observed in the RCM image correlates to naturally occurring variations in the refractive index of organelles and micro-structures in the skin. RCM
Figure 3 Comparison of images of reflectance confocal microscopy (Vivascope 1500) of subclinical actinic keratosis (left) and normal skin (right) of the same site in a patient before and after treatment. The image shows a field of 1.5 mm of the spinous layer of the epidermis. On the left side, the changes associated with subclinical actinic keratosis are atypical honeycomb with irregularity in the size and shape of corneocytes. In contrast the confocal image on the right shows a typical honeycomb.
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images allow the visualization of cellular and subcellular structures in the skin, similar to the detail seen in histology sections, but without the need for an invasive biopsy procedure.16 RCM has been used in the diagnosis of several dermatological conditions including melanoma and basal cell carcinoma.16 Reflectance confocal microscopy enables the histological changes that characterize AK to be imaged and so can be used in the diagnosis of this disease.6,17 RCM also enables the initial changes in epidermal morphology and cellular atypia to be visualized before the disease becomes clinically apparent and is therefore useful for the evaluation of AK field cancerization and the detection of subclinical AK (Fig. 3).18 The main RCM features of clinical AK lesions are: disruption and parakeratosis in the stratum corneum; pleomorphism and architectural disruption in the stratum granulosum and stratum spinosum with loss of the normal honeycomb pattern; and solar elastosis and increased vascularity or blood vessel dilatation in the superficial dermis.6,16–18 Of these features, cellular pleomorphism and architectural disarray are considered the best predictors of AK.6 The principal RCM features of subclinical AK lesions are pleomorphism and architectural disruption in the stratum spinosum (Fig. 3), but not in the stratum granulosum, and solar elastosis.18 Reflectance confocal microscopy can also be used in the differential diagnosis of AK and SCC, which is important since the two types of lesions require different therapeutic approaches. A study which compared RCM images of AK lesions and SCC demonstrated that SCC shows an increased frequency of abnormal RCM features compared with AK.19 The key RCM features of SCC are the presence of an atypical honeycomb pattern and round nucleated cells corresponding to atypical keratinocytes in the stratum spinosum and stratum granulosum, and round blood vessels crossing the dermal papilla. These blood vessels are
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scarcer in AK since these lesions are smaller and less developed neoplasms.19 Reflectance confocal microscopy allows the effects of AK treatments such as imiquimod or diclofenac sodium to be monitored by non-invasively examining subclinical and clinical lesions in vivo over time.18,20–22 An RCM investigation into the effects of imiquimod on actinic field cancerization demonstrated that this field-directed treatment unmasks previously invisible subclinical lesions and is able to effectively treat both clinical and subclinical lesions. Furthermore, RCM can detect any residual subclinical disease remaining after initial treatment with imiquimod and so can identify patients who may benefit from additional cycles of therapy.18 After 2 weeks of imiquimod treatment, RCM imaging of clinical and subclinical lesions revealed the presence of inflammatory cells in the dermis and epidermis, which correspond to the immunomodulatory response induced by this treatment. Four weeks after treatment with imiquimod was completed, RCM imaging demonstrated that clinical and subclinical lesions had been cleared, e.g. by revealing that the typical honeycomb pattern at the level of stratum granulosum and spinosum had been re-established.18 Similarly, RCM imaging revealed that 2 weeks of treatment with diclofenac sodium resulted in a significant decrease in scaling and in the atypical honeycomb pattern in AK patients.20 RCM has also been used to non-invasively diagnose actinic cheilitis (AK on the lip) and to visualize the response to treatment with diclofenac sodium by demonstrating the absence of cellular atypia and rearrangement of the epidermal architecture.21
High-definition optical coherence tomography Optical coherence tomography (OCT) is a non-invasive imaging technique that has been used to diagnose and monitor a variety
Figure 4 High-definition optical coherence tomography slice imaging of normal skin (top panel) and skin from a patient with actinic keratosis (lower panel) (Skintell, AGFA) (field of 1 mm in diameter). In the image of normal skin, the epidermis is regular with normal thickness and the dermo-epidermal junction is clear and has a typical shape. In contrast, in the image of the patient with actinic keratosis, the thickness of the epidermis is irregular. The stratum corneum is thickened with an increase in contrast due to keratin and the dermo-epidermal junction is flat. Epid, epidermis; DEJ, dermo-epidermal junction.
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of dermatological disorders (e.g. AK, psoriasis, contact dermatitis, cutaneous lupus erythematosus, basal cell carcinoma).23 It is based on the interference of infrared radiation and tissue samples and is used to generate real-time 2-D or 3-D cross-sectional images of biological tissues such as the skin. OCT allows noninvasive in vivo investigation of the stratum corneum, the epidermis, the dermo-epidermal junction and the upper dermis.23 The OCT technique provides real-time skin images to a depth of several millimetres depending on the tissue studied and to a resolution of a few micrometres (commonly 5–10 lm), but cannot display distinct morphological or cellular features.23 More recently, high-definition OCT (HD-OCT) has been developed to provide improved lateral and axial resolution of 3 lm, although with a reduced penetration depth of 750 lm.24,25 This resolution allows visualization of architectural changes and cellular features. With HD-OCT, both horizontal (en-face mode) and conventional vertical (slice mode) imaging can be performed. Recent studies have shown that HD-OCT enables the in vivo non-invasive diagnosis of AD, allows the grading of different types of AK lesions and the identification of subclinical lesions.25,26 In addition, the technique was shown to offer additional information in the diagnosis of AK compared with regular OCT in both the conventional slice (vertical) and in the en-face (horizontal) imaging modes.25 En-face HD-OCT imaging of AK lesions reveals similar features to RCM such as disruption of the stratum corneum; architectural disarray in the epidermis with an atypical honeycomb pattern; cellular and nuclear polymorphism in the stratum granulosum and stratum spinosum; and bright irregular bundles in the superficial dermis. In contrast, en-face HD-OCT imaging of healthy skin reveals a regular honeycomb pattern in the stratum granulosum and stratum spinosum, and shows no interruption of the stratum corneum.25 Vertical slice imaging of AK lesions reveals an irregular entrance signal, lack of distinct layering, white streaks and dots, and grey areas. These features contrast to vertical slice images of healthy skin which show distinct layering of the epidermis and dermis (Fig. 4).25 The images obtained from HD-OCT of AK lesions were found to correlate with the features identified by conventional histology. For example, the disruption of the stratum corneum detected by HD-OCT imaging correlates with the parakeratosis identified by histology, and the architectural disarray in the stratum granulosum and stratum spinosum seen in HD-OCT images correlates with the destruction of the epidermal structure observed in histology.25,26 The extent of the disruption of the honeycomb pattern in the epidermis observed by HD-OCT was shown to correlate with the severity of AK. For example, subclinical lesions are characterized by a mildly atypical honeycomb pattern in the bottom third of the epidermis, whereas clinical lesions have more extensive disruption of the honeycomb pattern.26 HD-OCT imaging of sun-damaged skin surrounding AK lesions shows features of solar elastosis and a slightly irregular honeycomb pattern.26
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Comparison of RCM and HD-OCT The respective advantages of RCM and HD-OCT mean that these techniques generate complementary information which together can provide a complete picture of the full extent and burden of a patient’s disease. The main advantage of RCM is that it provides images of greater resolution than HD-OCT (1.5 vs. 3 lm). Although both imaging technologies can be used to identify cells in the epidermis,27 the improved resolution of RCM means that both cellular and subcellular morphology can be visualized in detail.25,26 The key benefit of HD-OCT is that it provides images to a greater depth than RCM (750 vs. 250 lm) and so allows imaging of deeper layers of the skin. In addition, unlike RCM which can only image horizontal sections of skin, HD-OCT provides both horizontal and vertical images of skin and may also be used for rapid 3-D imaging.25–27
Conclusions Biopsy sampling together with histopathological analysis is not feasible for the detailed investigation of field cancerization which characterizes AK. In contrast, new imaging technologies such as RCM and HD-OCT allow non-invasive objective morphological characterization of AK field cancerization and assessment of response to field-directed treatments. Together, the results from these new imaging techniques clearly demonstrate that the disease burden of AK consists of both clinical and subclinical lesions across the entire sun-exposed field. The consequence of this pathophysiology is that the target for the treatment of AK needs to be the detection and elimination of all clinical and subclinical lesions across the entire sun-exposed field.
Acknowledgements Editorial assistance in the preparation of this manuscript was provided by David Harrison, Medscript Communications and was funded by Meda Pharma GmbH & Co. KG.
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