Molecular Diagnostics Rotation

(1 Week)

While our understanding of the causes and mechanisms that govern the development of human diseases is far from complete, molecular diagnostics is the most rapidly expanding subspecialty of pathology. Molecular diagnostics refers to the area of clinical laboratory medicine in which the detection and analysis of nucleic acids is applied to diagnose disease, to predict the prognosis of disease, to guide therapy, and to evaluate the susceptibility to disease before clinical presentation of disease is evident. Historically, advancements in molecular diagnostics reflect the tremendous technological breakthroughs originating in the field of molecular biology.

The Molecular Diagnostics rotation in Pathology provides the medical student a broad overview of molecular theory and exposure to molecular techniques, a forum to understand clinical applications of various molecular tests, and a relevant experience in both conducting and interpreting molecular diagnostic testing. The growing significance of the field of molecular pathology and its clinical impact will be emphasized. Examples of some of the clinical applications of molecular pathology, medical students will observe are briefly summarized.

Use of genetic markers for the purposes of inclusion or exclusion of individuals in forensic investigations is widely documented. Human identity testing can be accomplished through the analysis of genomic polymorphisms such as variable number tandem repeat (VNTR) or short tandem repeat (STR) loci. These loci are comprised of a relatively constant core DNA sequence which is repeated, consecutively, a variable number of times within a discreet genetic locus. STR/VNTR loci provide a definitive set of genetic polymorphisms with large discriminatory value between individuals that are also utilized in numerous clinical settings, including the assessment of a patient after stem cell transplantation (see example below).

The molecular pathology tests performed most frequently in clinical laboratories today are in the field of infectious diseases. Marked improvement in the sensitivity of nucleic acid-based detection of infectious agents, dynamic quantification ranges and the rapid turnaround time as compared with some culture or antigen detection methods has argued for a stronger representation of molecular techniques in many laboratories. Molecular methods are beneficial in the detection of infectious agents that are not possible to cultivate, dissemination of types based on genetic differences (see HSV I and II examples below), identification of antibiotic or antiviral resistance genes, and identification of toxin genes and are more frequently being utilized in a majority of laboratories. Additionally, the ability to quantitate infectious organisms can be advantageous to evaluate the efficacy of therapy (see HBV example below), to screen for and establish resistant organisms and to guide changes to therapy. Establishment of real time PCR based techniques and platforms allows for more reliable quantitative results and the ability to achieve more efficient turn around time in obtaining results. Consequently, utilization of molecular methods in infectious disease testing is having a major impact in the diagnosis, treatment, assessment and prognosis of our patients.

Substantial advances first in the knowledge of leukemias and lymphomas, embodied in part in the increasingly detailed information regarding the genetic alterations contributing to the development of these neoplasms, have been particularly important in the field of hematopathology. Similar advances in our understanding of the molecular genetics of solid tumors are also having a significant impact on the pathologist’s approach to these neoplasms. Discoveries of inherited alterations in tumor suppressor genes and genes encoding proteins responsible for DNA repair and their association with neoplasms, such as breast and colon adenocarcinomas, have opened a new arena of clinical assays for cancer predisposition assessment. An important and expanding aspect of functional genomics assays is the finding of individual proteins whose targeting is deleterious for the tumor cell, opening the door to the development of drugs that by interfering with the action of unique tumor markers may be therapeutically relevant as modes of treatment. Contrastingly, the use of molecular analysis to yield the likelihood of tumors not responding to treatment prevents the unnecessary use of expensive therapies that will not benefit our patients, the avoidance of unnecessary, adverse side effects and the ability to proceed more quickly to alternative beneficial treatments. In the example depicted below, the detection of a majority of mutations in codons 12, 13 and 61 of the KRAS gene are reported to correlate with resistance to anti-EGFR monoclonal antibody therapies, such as cetuximab (ERBITUX®) and panitumumab (Vectibix®), in patients with colorectal adenocarcinoma and non-small cell lung carcinoma. Regardless of tumor type, greater efforts in comprehensive molecular profiling of tumors, coupled with a growing portfolio of targeted drugs under clinical development and already approved, offers hope for an overall more effective and individualized anti-cancer therapy.