The same holds true for MSH2 and its binding partner MSH6. Table 3 Immunohistochemical staining patterns and interpretation for MMR proteins Figure 20 A MSI tumor showing loss of MLH1 (A) and PMS2 (D) protein expression, and normal expression of MSH2 (B) and MSH6 (C). Note the presence of positive staining in benign colonic crypts and inflammatory cells, which serve as good internal controls for the … The sensitivity of PCR-based MSI test using the Bethesda panel ranges from 55% to 84% for Inhibitors,research,lifescience,medical the detection of mutations in different MMR gene.

The sensitivity is increased if three or more mononucleotide repeat markers are used. The specificity of MSI test is 90%. Immunohistochemistry has been accepted as a reliable substitute for MSI with a concordance rate of >90%. It also

provides additional information over PCR-based MSI test in Inhibitors,research,lifescience,medical that it allows gene-specific DNA sequence analysis based on the staining pattern. However, immunohistochemistry may miss rare MSI cases that are caused by germline mutations by other genes and does not discriminate germline mutation from epigenetic alteration when loss of MLH1 protein expression is detected. Thus, the most recent recommendation is to perform both PCR-based MSI test and immunohistochemistry in order to minimize the chance of Erlotinib manufacturer missing the diagnosis of Lynch syndrome (117). It is also recently advocated to test Inhibitors,research,lifescience,medical all Inhibitors,research,lifescience,medical newly diagnosed colorectal cancers regardless of patient’s age and family history because ~25% of the patients with Lynch syndrome do not meet Amsterdam Criteria II or Bethesda guidelines (117). In that setting, only one test, either immunohistochemistry or MSI analysis,

may be performed because the cost of the tests will become Inhibitors,research,lifescience,medical an issue. KRAS testing Mutations in the KRAS (Kirsten rat sarcoma viral oncogene homolog) gene lead to expression of a constitutively activated KRAS protein, which are detected in ~40% of colorectal cancers (2,118). As a critical downstream molecule in the epidermal growth factor receptor (EGFR) signaling pathway, mutant KRAS renders tumors resistant to EGFR-targeted therapies (2,119-121). As a result, the American Society for Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) have recommended mutation analysis of the KRAS gene for Metalloexopeptidase candidate patients who will receive anti-EGFR therapies (122,123). Greater than 95% of KRAS mutations occur in codons 12 and 13 in exon 2 (118,124,125), and thus PCR-based methodologies designed to detect KRAS mutations are primarily for these mutations. Mutations can also occur in other loci such as codons 61 and 146 (126), but they are generally not screened because of rarity. Clinically available real-time PCR-based methods include allele-specific amplification assay and post-PCR melting curve analysis.