Contributions of molecular analysis to the diagnosis and treatment of gastrointestinal neoplasms.

This review discusses the role of molecular analysis in the diagnosis and treatment of gastrointestinal (GI) neoplasms. It is divided into 3 sections. The first section describes clinical applications of 11 immunohistochemical stains (p53, HER2, KIT, SDHB, SMAD4, beta-catenin, L-FABP, MLH1, PMS2, MSH2, and MSH6), the results of which directly reflect underlying genetic or epigenetic events. These applications are mainly diagnostic but in a few instances are predictive. Germline mutation testing is a diagnostic cornerstone in the hereditary cancer predisposition syndromes (HCPSs). Section two will describe the genotype and phenotype of 8 HCPSs presenting in the GI tract. Where available, guidelines based on evidence and/or expert opinion as to whom to test are presented. With our ever-expanding knowledge of the molecular genetic basis of cancer and an increasingly "biologic-oriented" therapeutic armamentarium, pathologists play a vital role in directing molecular-based predictive testing. The final section will discuss the 4 most mature examples in the GI tract: (1) HER2 testing to select patients with advanced gastroesophageal adenocarcinoma for anti-HER2 therapy, (2) KIT and PDGFRA mutation analysis to direct tyrosine kinase inhibitor therapy in gastrointestinal stromal tumor, (3) DNA mismatch repair function testing to determine the applicability of adjuvant chemotherapy in patients with stage II colorectal cancer (CRC), and (4) KRAS mutation analysis and related testing to determine the appropriateness of anti-EGFR monoclonal antibody therapy in patients with metastatic CRC.