Recent Advances in Histopathology of Gastrointestinal Cancers: Prognostic and Therapeutic Assessment of Colorectal Cancers

Abstract

The genetics and molecular biology, precursor lesions and predisposing conditions, and hereditary syndromes of gastrointestinal cancers, especially colorectal cancers, are well characterized. Fifteen to twenty percent of sporadic colorectal carcinomas have microsatellite instability (MSI; replication-error phenotype), characterized by defective DNA repair resulting in alterations of short tandem repeat sequences, including mononucleotide, dinucleotide, and tetranucleotide repeats. This is due to alteration of mismatch repair enzymes. Patients with colorectal cancers with MSI have a better prognosis than do those without. In contrast, about 50% to 60% of colorectal cancers have loss of the long arm (q) of chromosome 18, the chromosomal location of the deleted in colorectal cancer, SMAD4, and SMAD2 genes. Chromosome 18q loss has been associated with poor outcome in patients with colorectal cancer. Growth factors and growth factor receptors play a major role in the development and progression of cancer. Gastrointestinal cancers express epidermal growth factor receptor (EGFR) and related receptors that activate intrinsic tyrosine kinase activity and result in signals of cell proliferation. This activity can be modulated by a variety of therapeutic options, including monoclonal antibody against EGFR or related receptors and selective inhibition of tyrosine kinase activity. Immunohistochemical analysis for EGFR can select patients who have EGFR-overexpressing gastrointestinal cancer and thus are potential candidates for anti-EGFR therapy.