Such classification is important because this molecular signature provides clues to the natural history of the tumor and optimal patient management. A classic example is microsatellite instability (MSI) which occurs in approximately 15% of colorectal Selleckchem LDK378 cancers as a result of mismatch repair deficiency. Following inactivation of one of a family of mismatch repair genes (MLH1, MSH2, MSH6 or PMS2), the cell’s ability to repair frameshift
errors in nucleotide repeat tracts becomes compromised. This distinct subset of tumors can be identified either using molecular diagnostics (by the resultant instability in length of microsatellite repeat tracts) or by immunohistochemical staining for loss of mismatch repair proteins. Following the discovery of MSI almost 2 decades ago, this interesting phenomenon has translated into an important biomarker routinely used to inform buy Enzalutamide patient management. It is now well accepted that tumors showing MSI share clinical features; these include predilection for the proximal colon, female sex and improved prognosis. Histologically, MSI-related tumors are often poorly differentiated,
mucinous and have tumor infiltrating lymphocytes. In fact, histological criteria alone have been shown to be highly sensitive for detecting MSI.1 Age of onset is bimodally distributed reflecting, in general, either early-onset hereditary or late-onset sporadic cases. Recognition of this dichotomy is critical for managing treatment and surveillance regimes. Hereditary cases termed hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome arise due to germline mutation of a mismatch repair gene. Usually before the fifth decade
the second copy of the gene is mutated or deleted in a colonocyte, resulting in rapid progression to cancer. Identification and close surveillance of germline mutation carriers is therefore critical for disease prevention. Sporadic MSI cancers follow a very different morphological and molecular pathway to their hereditary cousins. In contrast to Lynch cancers that originate in traditional adenomas, sporadic MSI cancers arise from sessile serrated adenomas (SSA).2 These are a distinct subtype of serrated polyps distinguished by characteristic architectural features, including basal crypt dilation, crypt branching and abnormal proliferation.3 These lesions are frequently Bay 11-7085 large, flat, covered with mucin and arise in the proximal colon, all features that present colonoscopic challenges for visualization and removal. Although it is not known what proportion of SSA will transform to cancer, at least a subset definitely has malignant potential; in some cases, progression may be rapid.4 Current best practice dictates that all but diminutive distal hyperplastic polyps be removed for histological examination and those which are SSA treated as adenomas for surveillance purposes.5 The majority of SSA and sporadic MSI cancers have mutation of the BRAF oncogene.