Histopathological Predictors of Microsatellite Instability in Colorectal Cancer-a Tertiary Care Center Experience.

Microsatellite instability (MSI) has a therapeutic and prognostic implication in colorectal carcinomas (CRCs). It can be detected either by immunohistochemistry (IHC) or molecular studies. In developing countries, a significant proportion of the patients experience financial constraints limiting the utilization of healthcare facilities. We aimed to identify the possible clinicopathological variables which can be used as predictors of microsatellite instability in such patients. CRC cases received for MSI detection by IHC (for 1 and 1/2 years) were included. A panel of four IHC markers (anti-MLH1, anti-PMS2, anti-MSH2, and anti-MSH6) was used. Confirmation by the molecular study was recommended in all the IHC-proven MSI cases. Various clinicopathological parameters were evaluated as predictors of MSI. Microsatellite instability was detected in 40.6% (30/74) cases with MLH1 and PMS2 dual loss in 27% cases, MSH2 and MSH6 dual loss in 6.8%, loss of all four MMR proteins in 2.7%, and isolated PMS2 loss in 4.1%. MSI-H expression was shown by 36.5% cases with only 4.1% cases showing MSI-L expression. The age cut-off value to differentiate both the study groups (MSI vs MSS) was 63 years with a sensitivity of 47.7% and specificity of 86.7%. ROC curve showed an area under the curve of 0.65 (95% CI, 0.515-0.776;