© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
J Cutan Pathol 2013: 40: 921–923 doi: 10.1111/cup.12238 John Wiley & Sons. Printed in Singapore
Journal of Cutaneous Pathology
Editorial
Connect the dots Keywords: CD19, CD99, dot-like, immunoperoxidase, Merkel cell carcinoma It has been known for roughly three decades that dot-like paranuclear (or, alternatively and reasonably equivalently, perinuclear) keratin immunopositivity can be utilized as a tool for the immunoperoxidase confirmation of a diagnosis of Merkel cell carcinoma.1 Utilized widely as a diagnostic tactic in the early 1990s, the significance of dots of paranuclear keratin expression has been largely superseded in the collective analytical mindset by the exceedingly popular use of CK20 (cytokeratin 20) immunohistochemistry, which also commonly manifests with dots of juxtanuclear positivity in the context of MCC.2,3 (Editor’s note: it is helpful to recall the past steady reliability of generic ‘dot’ keratin positivity as a tool to recognize MCC when dealing with the occasional case in which more modern staining techniques, discussed in the sentences that follow, prove disappointing or confusing.) Since 1993 or so, it has been reasonably clear that neurofilament immunohistochemistry provides a highly effective means to demonstrate cutaneous neuroendocrine lineage, as cytoplasmic dots of neurofilament positivity are both sensitive and specific for the detection of MCC.4 In head-to-head comparison of CK20 and neurofilament for recognition of MCC, neurofilament is superior,5,6 and the combination of the two reagents provides an extremely sensitive detection method.5 Neurofilament is also less prone than CK20 to exhibit the potentially misleading punctate paranuclear positivity that can be occasionally observed in association with selected non-cutaneous neuroendocrine carcinomas, such as ovarian or salivary gland small cell carcinoma.7 Sadly, however, neurofilament immunohistochemistry has never achieved acclaim as a diagnostic approach. CK20 remains the most popular kid on the schoolyard. When the question of is this Merkel cell carcinoma? is broached in the evaluation of a given case, CK20 staining is commonly combined with the evaluation of multiple other epitopes associated with neuroendocrine lineage, such as neuron specific enolase (NSE), CD56, chromogranin, and synaptophysin. Such a panel staining approach is probably inefficient
and occasionally can prove to be profoundly detrimental or confusing, diagnostically speaking, as false positive labeling of non-neuroendocrine carcinomas, including basal cell carcinoma, can be found. Additionally, the four determinants mentioned in the last clause of the first sentence of this paragraph suffer from poor specificity, as they label both cutaneous and non-cutaneous neuroendocrine carcinomas. If a staining algorithm intended to identify a cutaneous metastasis of extracutaneous neuroendocrine carcinoma is desired, probably the deployment of thyroid transcription factor-1 (TTF1) in conjunction with neurofilament and CK20 is most advantageous, although vigilance against the rare pitfall of of MCC with a TTF1-positive immunophenotype remains a necessity.8 Intriguingly, MCC cells exhibiting punctate paranuclear dots of chromogen can be spotted (pun intended) utilizing a variety of immunoreagents, and the phenomenon is not restricted to stains that detect intermediate filaments. Juxtanuclear dot-like deposition of CD23, insulin-like growth factor-I receptor, and CD99 has been reported,9 – 11 and dot-like paranuclear CK19 expression can be found routinely as well.12 Whether or not immunohistochemistry is identifying authentic juxtanuclear deposition of multiple epitopes – or whether instead there is merely a sticky filamentous ball in the cytoplasm of MCC cells that merely binds multiple epitopes, nonspecifically – has not been addressed in any meaningful way to the knowledge of this observer, but the latter explanation seems most likely (and, if this hypothesis is true, then it should be anticipated that additional diverse reagents exhibiting dot-like labeling of MCC will be found). In a similar vein, although CK19 has been put forth as a stem cell marker, given the hodgepodge of immunoreagents that exhibit paranuclear positivity, it seems likely that dot-like CK19 expression cannot be taken as trustworthy confirmation of a stem cell role in the pathogenesis of MCC.12 Rather, dots of CK19 expression are probably exactly analogous
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Editorial to dots of CK20 or neurofilament: they provide diagnostic acuity but not insight into pathogenesis. Although juxtanuclear dots of chromogen deposition are commonly associated with neuroendocrine carcinoma, it is important to recognize that this immunomorphologic phenomenon is not restricted to MCC. As an illustration of its heterogeneity, paranuclear punctate neurofilament expression can be identified in association with synovial sarcoma,13 and paranuclear dots of neurofilament or desmin can also be observed in association with rhabdomyosarcoma or rhabomyosarcomatous elements.14,15 Elsewhere in this issue of the JCP, Luzar and Calonje additionally report the novel observation of paranuclear dot-like keratin (MNF116) expression in cutaneous myoepithelioma.16 It seems likely that punctate positivity will be uncovered in other diagnostic contexts as well. In short, paranuclear dots are not unique to neuroendocrine carcinoma. How, then, should one connect the dots with respect to paranuclear positivity? In the mind of this observer, it remains abundantly clear that seeking punctate chromogen deposition represents the ideal method for the diagnosis of MCC, and neurofilament, rather than CK20, is probably the single most effective diagnostic tool on the workbench (if only one stain can be done, neurofilament should be the one). The combination of neurofilament, CK20, and TTF1 seems likely to provide high diagnostic efficiency while simultaneously addressing extracutaneous neuroendocrine carcinoma as a possibility in the differential diagnosis. Use of commonly available stains such as CD23, CK19, and generic keratin can be considered on an occasional basis if MCC
remains strongly suspected, based upon conventional histopathologic assessment, and if neurofilament and CK20 have proven to be negative. Although CD99 remains an additional option, the fact that its reactivity is often weak (personal observation) makes it of lesser diagnostic value. Immunostains that have not captured the public imagination, such as insulin-like growth factor-I receptor, hold no specific role. Immunoreagents with lesser specificity, such as chromogranin, synaptophysin, CD56, and NSE, may be best reserved for exceptional circumstances. Lastly, any dermatopathologist or histopathologist should be mindful of the fact that paranuclear dots can be observed in multiple immunopathologic settings, including neuroendocrine carcinoma and various myoid tumors or sarcomas. That said, it seems likely that obvious histomorphologic differences amongst such varied entities will limit diagnostic confusion in most instances. Postscript: In a recent editorial,17 it was noted that toxic erythema of chemotherapy (TEC) was first recognized as a ‘peculiar acral erythema’ by Burgdorf and colleagues.18 Correspondence with Walter Burgdorf indicates that this is a common attribution, but in actual fact Richard Zuehlke made the seminal observation some eight years prior.19 The Journal thanks Dr. Burgdorf for setting the record straight. Timothy H. McCalmont, Editor-in-Chief San Francisco, CA
References 1. Layfield L, Ulich T, Liao S, Barr R, Cheng L, Lewin KL. Neuroendocrine carcinoma of the skin: an immunohistochemical study of tumor markers and neuroendocrine products. J Cutan Pathol 1986 Aug; 13: 268. 2. Liu Y, Mangini J, Saad R, et al. Diagnostic value of microtubule-associated protein-2 in Merkel cell carcinoma. Appl Immunohistochem Mol Morphol 2003; 11: 326. 3. Keehn CA, Saeed S, Bickle K, Khalil FK, Morgan MB. Expression of insulin-like growth factor-I receptor in primary cutaneous carcinomas. J Cutan Pathol 2004 May; 31: 368. 4. Shah IA, Netto D, Schlageter MO, Muth C, Fox I, Manne RK. Neurofilament immunoreactivity in Merkel-cell tumors
922
5.
6.
7.
8.
a differentiating feature from small-cell carcinoma. Mod Pathol 1993; 6: 3. McCalmont TH. Paranuclear dots of neurofilament reliably identify Merkel cell carcinoma. J Cutan Pathol 2010; 37: 821. Acebo E, Vidaurrazaga N, Varas C, BurgosBretones JJ, Diaz-Perez JL. Merkel cell carcinoma a clinicopathological study of 11 cases. J Eur Acad Dermatol Venereol 2005; 19: 546. Rund CR, Fischer EG. Perinuclear dot-like CK20 staining in small cell neuroendocrine carcinoma of the ovary (pulmonary-type). Appl Immunohistochem Mol Morphol 2006; 14: 244. Ishida M, Okabe H. Merkel cell carcinoma concurrent with Bowen’s disease: two cases, one with an unusual immunophenotype. J Cutan Pathol 2013; 40: 839.
9. Carvalho J, Fullen D, Lowe L, Su L, Ma L. Comparison of CD23 staining patterns in Merkel cell carcinoma and non-cutaneous small cell carcinoma. J Cutan Pathol 2009; 36: 206. 10. Keehn CA, Saeed S, Bickle K, Khalil FK, Morgan MB. Expression of insulin-like growth factor-I receptor in primary cutaneous carcinomas. J Cutan Pathol 2004; 31: 368. 11. Rajagopalan A, Browning D, Salama S. CD99 expression in Merkel cell carcinoma a case series with an unusual paranuclear dot-like staining pattern. J Cutan Pathol 2013; 40: 19. 12. Abbas O, Bhawan J. Expression of stem cell markers nestin and cytokeratin 15 and 19 in cutaneous malignancies. J Eur Acad Dermatol Venereol 2011; 25: 311. 13. Folpe AL, Schmidt RA, Chapman D, et al. Poorly differentiated synovial sarcoma:
Editorial immunohistochemical distinction from primitive neuroectodermal tumors and high-grade malignant peripheral nerve sheath tumors. Am J Surg Pathol 1998; 22: 673. 14. Folpe AL, McKenney JK, Bridge JA, Weiss SW. Sclerosing rhabdomyosarcoma in adults: report of four cases of a hyalinizing, matrix-rich variant of rhabdomyosarcoma that may be confused with osteosarcoma, chondrosarcoma, or angiosarcoma. Am J Surg Pathol 2002; 26: 1175.
15. Adhikari LA, McCalmont TH, Folpe AL. Merkel cell carcinoma with heterologous rhabdomyoblastic differentiation: the role of immunohistochemistry for Merkel cell polyomavirus large T-antigen in confirmation. J Cutan Pathol 2012; 39: 47. 16. Luzar B, Calonje E. Paranuclear dot-like cytokeratin MNF116 positivity in cutaneous myoepithelioma. J Cutan Pathol 2013; 40: 982.
17. McCalmont T. TEC. J Cutan Pathol 2013; 40: 785. 18. Burgdorf WH, Gilmore WA, Ganick RG. Peculiar acral erythema secondary to highdose chemotherapy for acute myelogenous leukemia. Ann Intern Med 1982; 97: 61. 19. Zuehlke RI. Erythematous eruption of the palms and soles associated with mitotane therapy. Dermatologica 1974; 148: 90.
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J Cutan Pathol 2013: 40: 921–923 doi: 10.1111/cup.12238 John Wiley & Sons. Printed in Singapore
Journal of Cutaneous Pathology
Editorial
Connect the dots Keywords: CD19, CD99, dot-like, immunoperoxidase, Merkel cell carcinoma It has been known for roughly three decades that dot-like paranuclear (or, alternatively and reasonably equivalently, perinuclear) keratin immunopositivity can be utilized as a tool for the immunoperoxidase confirmation of a diagnosis of Merkel cell carcinoma.1 Utilized widely as a diagnostic tactic in the early 1990s, the significance of dots of paranuclear keratin expression has been largely superseded in the collective analytical mindset by the exceedingly popular use of CK20 (cytokeratin 20) immunohistochemistry, which also commonly manifests with dots of juxtanuclear positivity in the context of MCC.2,3 (Editor’s note: it is helpful to recall the past steady reliability of generic ‘dot’ keratin positivity as a tool to recognize MCC when dealing with the occasional case in which more modern staining techniques, discussed in the sentences that follow, prove disappointing or confusing.) Since 1993 or so, it has been reasonably clear that neurofilament immunohistochemistry provides a highly effective means to demonstrate cutaneous neuroendocrine lineage, as cytoplasmic dots of neurofilament positivity are both sensitive and specific for the detection of MCC.4 In head-to-head comparison of CK20 and neurofilament for recognition of MCC, neurofilament is superior,5,6 and the combination of the two reagents provides an extremely sensitive detection method.5 Neurofilament is also less prone than CK20 to exhibit the potentially misleading punctate paranuclear positivity that can be occasionally observed in association with selected non-cutaneous neuroendocrine carcinomas, such as ovarian or salivary gland small cell carcinoma.7 Sadly, however, neurofilament immunohistochemistry has never achieved acclaim as a diagnostic approach. CK20 remains the most popular kid on the schoolyard. When the question of is this Merkel cell carcinoma? is broached in the evaluation of a given case, CK20 staining is commonly combined with the evaluation of multiple other epitopes associated with neuroendocrine lineage, such as neuron specific enolase (NSE), CD56, chromogranin, and synaptophysin. Such a panel staining approach is probably inefficient
and occasionally can prove to be profoundly detrimental or confusing, diagnostically speaking, as false positive labeling of non-neuroendocrine carcinomas, including basal cell carcinoma, can be found. Additionally, the four determinants mentioned in the last clause of the first sentence of this paragraph suffer from poor specificity, as they label both cutaneous and non-cutaneous neuroendocrine carcinomas. If a staining algorithm intended to identify a cutaneous metastasis of extracutaneous neuroendocrine carcinoma is desired, probably the deployment of thyroid transcription factor-1 (TTF1) in conjunction with neurofilament and CK20 is most advantageous, although vigilance against the rare pitfall of of MCC with a TTF1-positive immunophenotype remains a necessity.8 Intriguingly, MCC cells exhibiting punctate paranuclear dots of chromogen can be spotted (pun intended) utilizing a variety of immunoreagents, and the phenomenon is not restricted to stains that detect intermediate filaments. Juxtanuclear dot-like deposition of CD23, insulin-like growth factor-I receptor, and CD99 has been reported,9 – 11 and dot-like paranuclear CK19 expression can be found routinely as well.12 Whether or not immunohistochemistry is identifying authentic juxtanuclear deposition of multiple epitopes – or whether instead there is merely a sticky filamentous ball in the cytoplasm of MCC cells that merely binds multiple epitopes, nonspecifically – has not been addressed in any meaningful way to the knowledge of this observer, but the latter explanation seems most likely (and, if this hypothesis is true, then it should be anticipated that additional diverse reagents exhibiting dot-like labeling of MCC will be found). In a similar vein, although CK19 has been put forth as a stem cell marker, given the hodgepodge of immunoreagents that exhibit paranuclear positivity, it seems likely that dot-like CK19 expression cannot be taken as trustworthy confirmation of a stem cell role in the pathogenesis of MCC.12 Rather, dots of CK19 expression are probably exactly analogous
921
Editorial to dots of CK20 or neurofilament: they provide diagnostic acuity but not insight into pathogenesis. Although juxtanuclear dots of chromogen deposition are commonly associated with neuroendocrine carcinoma, it is important to recognize that this immunomorphologic phenomenon is not restricted to MCC. As an illustration of its heterogeneity, paranuclear punctate neurofilament expression can be identified in association with synovial sarcoma,13 and paranuclear dots of neurofilament or desmin can also be observed in association with rhabdomyosarcoma or rhabomyosarcomatous elements.14,15 Elsewhere in this issue of the JCP, Luzar and Calonje additionally report the novel observation of paranuclear dot-like keratin (MNF116) expression in cutaneous myoepithelioma.16 It seems likely that punctate positivity will be uncovered in other diagnostic contexts as well. In short, paranuclear dots are not unique to neuroendocrine carcinoma. How, then, should one connect the dots with respect to paranuclear positivity? In the mind of this observer, it remains abundantly clear that seeking punctate chromogen deposition represents the ideal method for the diagnosis of MCC, and neurofilament, rather than CK20, is probably the single most effective diagnostic tool on the workbench (if only one stain can be done, neurofilament should be the one). The combination of neurofilament, CK20, and TTF1 seems likely to provide high diagnostic efficiency while simultaneously addressing extracutaneous neuroendocrine carcinoma as a possibility in the differential diagnosis. Use of commonly available stains such as CD23, CK19, and generic keratin can be considered on an occasional basis if MCC
remains strongly suspected, based upon conventional histopathologic assessment, and if neurofilament and CK20 have proven to be negative. Although CD99 remains an additional option, the fact that its reactivity is often weak (personal observation) makes it of lesser diagnostic value. Immunostains that have not captured the public imagination, such as insulin-like growth factor-I receptor, hold no specific role. Immunoreagents with lesser specificity, such as chromogranin, synaptophysin, CD56, and NSE, may be best reserved for exceptional circumstances. Lastly, any dermatopathologist or histopathologist should be mindful of the fact that paranuclear dots can be observed in multiple immunopathologic settings, including neuroendocrine carcinoma and various myoid tumors or sarcomas. That said, it seems likely that obvious histomorphologic differences amongst such varied entities will limit diagnostic confusion in most instances. Postscript: In a recent editorial,17 it was noted that toxic erythema of chemotherapy (TEC) was first recognized as a ‘peculiar acral erythema’ by Burgdorf and colleagues.18 Correspondence with Walter Burgdorf indicates that this is a common attribution, but in actual fact Richard Zuehlke made the seminal observation some eight years prior.19 The Journal thanks Dr. Burgdorf for setting the record straight. Timothy H. McCalmont, Editor-in-Chief San Francisco, CA
References 1. Layfield L, Ulich T, Liao S, Barr R, Cheng L, Lewin KL. Neuroendocrine carcinoma of the skin: an immunohistochemical study of tumor markers and neuroendocrine products. J Cutan Pathol 1986 Aug; 13: 268. 2. Liu Y, Mangini J, Saad R, et al. Diagnostic value of microtubule-associated protein-2 in Merkel cell carcinoma. Appl Immunohistochem Mol Morphol 2003; 11: 326. 3. Keehn CA, Saeed S, Bickle K, Khalil FK, Morgan MB. Expression of insulin-like growth factor-I receptor in primary cutaneous carcinomas. J Cutan Pathol 2004 May; 31: 368. 4. Shah IA, Netto D, Schlageter MO, Muth C, Fox I, Manne RK. Neurofilament immunoreactivity in Merkel-cell tumors
922
5.
6.
7.
8.
a differentiating feature from small-cell carcinoma. Mod Pathol 1993; 6: 3. McCalmont TH. Paranuclear dots of neurofilament reliably identify Merkel cell carcinoma. J Cutan Pathol 2010; 37: 821. Acebo E, Vidaurrazaga N, Varas C, BurgosBretones JJ, Diaz-Perez JL. Merkel cell carcinoma a clinicopathological study of 11 cases. J Eur Acad Dermatol Venereol 2005; 19: 546. Rund CR, Fischer EG. Perinuclear dot-like CK20 staining in small cell neuroendocrine carcinoma of the ovary (pulmonary-type). Appl Immunohistochem Mol Morphol 2006; 14: 244. Ishida M, Okabe H. Merkel cell carcinoma concurrent with Bowen’s disease: two cases, one with an unusual immunophenotype. J Cutan Pathol 2013; 40: 839.
9. Carvalho J, Fullen D, Lowe L, Su L, Ma L. Comparison of CD23 staining patterns in Merkel cell carcinoma and non-cutaneous small cell carcinoma. J Cutan Pathol 2009; 36: 206. 10. Keehn CA, Saeed S, Bickle K, Khalil FK, Morgan MB. Expression of insulin-like growth factor-I receptor in primary cutaneous carcinomas. J Cutan Pathol 2004; 31: 368. 11. Rajagopalan A, Browning D, Salama S. CD99 expression in Merkel cell carcinoma a case series with an unusual paranuclear dot-like staining pattern. J Cutan Pathol 2013; 40: 19. 12. Abbas O, Bhawan J. Expression of stem cell markers nestin and cytokeratin 15 and 19 in cutaneous malignancies. J Eur Acad Dermatol Venereol 2011; 25: 311. 13. Folpe AL, Schmidt RA, Chapman D, et al. Poorly differentiated synovial sarcoma:
Editorial immunohistochemical distinction from primitive neuroectodermal tumors and high-grade malignant peripheral nerve sheath tumors. Am J Surg Pathol 1998; 22: 673. 14. Folpe AL, McKenney JK, Bridge JA, Weiss SW. Sclerosing rhabdomyosarcoma in adults: report of four cases of a hyalinizing, matrix-rich variant of rhabdomyosarcoma that may be confused with osteosarcoma, chondrosarcoma, or angiosarcoma. Am J Surg Pathol 2002; 26: 1175.
15. Adhikari LA, McCalmont TH, Folpe AL. Merkel cell carcinoma with heterologous rhabdomyoblastic differentiation: the role of immunohistochemistry for Merkel cell polyomavirus large T-antigen in confirmation. J Cutan Pathol 2012; 39: 47. 16. Luzar B, Calonje E. Paranuclear dot-like cytokeratin MNF116 positivity in cutaneous myoepithelioma. J Cutan Pathol 2013; 40: 982.
17. McCalmont T. TEC. J Cutan Pathol 2013; 40: 785. 18. Burgdorf WH, Gilmore WA, Ganick RG. Peculiar acral erythema secondary to highdose chemotherapy for acute myelogenous leukemia. Ann Intern Med 1982; 97: 61. 19. Zuehlke RI. Erythematous eruption of the palms and soles associated with mitotane therapy. Dermatologica 1974; 148: 90.
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