I n t ro d u c t i o n : T h e I m p a c t o f Molecular Pathology on the Practice of Pathology Martin H. Bluth,


KEYWORD  Molecular pathology  Methods  Genomics  High throughput  Quality  Polymorphisms KEY POINTS  The Human Genome Project has paved the way for molecular pathology to profoundly influence general pathology practice and the understanding of pathobiology.  Molecular pathology techniques have provided medicine with accurate, sensitive, and rapid opportunities to diagnose and prognosticate disease in an unprecedented manner.  Application of molecular pathology to high-throughput automation is providing the ability for multiplex analysis and personalized medicine for individual patients.  Detection of abnormal genes and differences in patterns of gene expression can influence disease diagnosis and guide specific therapy.

The success of the Human Genome Project1 has expanded the field of molecular biology in an exponential manner. It has facilitated the identification of numerous novel genes of unknown function whose functions can now be determined and whose expressions can be monitored in different disease states. Whereas the discipline of pathology often refers to the rubric of the study of disease in general, molecular pathology refers to the analysis of nucleic acids and proteins to diagnose disease, predict the occurrence of disease, and predict the prognosis of diagnosed disease and guide therapy. Furthermore, recent advances in molecular pathology have positively affected the practice of medicine, especially diagnostic medicine. These changes result from abilities to clone disease-causing genes and the proteins that they encode and to detect the presence of these genes and proteins in the serum and other body fluids and tissues of patients, even though they may be present in minute quantities. This detection has been made possible by a veritable explosion of new, highly sensitive techniques involving amplification methods, such as polymerase chain reaction, branched DNA,

Karmanos Cancer Institute, Detroit Medical Center, Wayne State University School of Medicine, 8203 Scott Hall, 540 East Canfield, Detroit, MI 48201, USA E-mail address: [email protected] Clin Lab Med 33 (2013) 749–751 http://dx.doi.org/10.1016/j.cll.2013.09.002 labmed.theclinics.com 0272-2712/13/$ – see front matter Ó 2013 Elsevier Inc. All rights reserved.



fluorescence in situ hybridization, and mass spectroscopy, among others. The ability to streamline testing in a high-throughput manner, many of which have been automated, enables a single patient sample to be analyzed for multiple genes or proteins. Molecular pathology has afforded physicians the ability to drill down into interrogating disease states for causes related to chromosomal abnormalities, point mutations, polymorphisms, and the like, which can provide a personalized medicine approach to diagnose a wide spectrum of diseases. To this end, genes that encode drug-metabolizing enzymes, both activating and inactivating, and genes that encode ligands and receptors may show polymorphisms that either decrease or increase the therapeutic effectiveness or toxicity of drugs already in clinical use, thus accounting for some idiosyncratic responses previously not understood or predictable. As such, there have been major advances in testing patients for genetic expression of selective enzyme isoforms, allowing prediction of which drugs would be the most effective ones. As more polymorphisms are identified and correlated with individual patients’ response to treatment, pathologists will be called on increasingly to profile common polymorphisms in patients who are beginning therapy for common diseases, such as coronary artery disease, congestive heart failure, diabetes, thrombosis, hypertension, cancer, and infections. Mutations in select genes, produced by mutational events associated with, for instance, carcinogens and oncogenic viruses, often result in abnormal activation or overexpression of their encoded proteins. A laboratory’s definition of an individual patient’s genotype/phenotype, therefore, may determine the specific drugs and doses suitable for the patient. This evolution has placed pathologists in a more definitive position to determine appropriate therapy than traditional prediction of disease behavior based on morphology of lesions or culture characteristics of infectious organisms.2 Cancer is a major area in which the differential expression of specific genes characterizes particular tumors. New advances in molecular pathology related to gynecology, gastroenterology, dermatology, and hematology disciplines have provided unprecedented insight into the diagnosis of and screening for several different types of tumors. Similar advances have been accomplished in the disciplines of infectious disease and transfusion medicine. Clinical laboratories will likely be called on to perform such in-depth types of analyses with increasing frequency in the near future. A poignant example of this phenomenon is the diagnosis of leukemias and lymphomas. Morphologically and even immunophenotypically, it may prove difficult to distinguish among different types of each disease. Specific gene rearrangements and patterns of gene expression, however, now enable distinction of different types of disease in this regard. In addition, the relationships among diseases are also more sharply defined, and sometimes radically changed, by comparisons among the diseases’ gene expression profiles.3,4 As with all laboratory methods, excellent quality-assurance programs are required to ensure that molecular pathologic results are accurate and useful. Standardized methods for performance of the most common clinical molecular pathologic tests are published by the Clinical and Laboratory Standards Institute (formerly called the National Committee for Clinical Laboratory Standards). Use of these guidelines ensures that the data generated in molecular pathology laboratories are produced by methods that are the standard of excellent practice. Furthermore, interlaboratory comparison of test performance is provided by the College of American Pathologists (www.cap.org). Applying established standards of quality assurance and using molecular pathologic techniques with a thorough understanding of their respective strengths and weaknesses, pathologists will continue to capitalize on the opportunities

The Practice of Molecular Pathology

these techniques offer for improved patient care and the understanding of basic pathobiology. Financial costs inherent in operations pertaining to a molecular pathology laboratory need to be considered as well. Although molecular pathology tests can often incur higher costs than conventional testing approaches, there are proponents who argue that molecular testing may actually facilitate a decrease in unnecessary, lesssensitive, and less-specific tests, thereby perpetuating more targeted and appropriate therapy for patients in the long run.5,6 In summary, molecular diagnostic techniques provide new insights into disease that were never before possible. These techniques, however, must often be used in coordination with traditional laboratory tests. In cases of tissue pathology, the morphologic skills involved in histopathology and cytopathology must be used to ensure that appropriate cells and tissues are analyzed molecularly. Otherwise, analysis of other than targeted cells/tissues, despite high-quality technical methods interpreted with skill and experience, can lead to erroneous, sometimes dangerously misleading, results. In concert with classical pathology algorithms, molecular pathology affords unprecedented potential for refined, highly sensitive, rapid, and patient-specific characterization of disease. To this end, molecular pathologists are situated as proverbial diagnostic gatekeepers to ascertain and affirm that the evolution of molecular medicine is handled, processed, and interpreted appropriately for optimal patient care. REFERENCES

1. Venter JC, Adams MD, Myers EW, et al. The sequence of the human genome. Science 2001;291:1304–51. 2. Tozzi V. Pharmacogenetics of antiretrovirals. Antiviral Res 2010;85:190–200. 3. Bacher U, Kohlmann A, Haferlach T. Current status of gene expression profiling in the diagnosis and management of acute leukaemia. Br J Haematol 2009;145: 555–68. 4. Talaulikar D, Dahlstrom JE. Staging bone marrow in diffuse large B-cell lymphoma: the role of ancillary investigations. Pathology 2009;41:214–22. 5. Ross JS. The impact of molecular diagnostic tests on patient outcomes. Clin Lab Med 1999;19:815–31. 6. Ross JS. Financial determinants of outcomes in molecular testing. Arch Pathol Lab Med 1999;123:1071–5.


Introduction: the impact of molecular pathology on the practice of pathology.

Molecular pathology is affecting and influencing the entire clinical laboratory. Furthermore, the union of pathology and molecular medicine continues ...
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