The Registry Partners November 2020 CTR Coding Break reviews discusses extent of disease fields pertaining to colon, rectum and rectosigmoid junction as well as the site-specific data item titled microsatellite instability (MSI). EOD Primary Tumor is used to code contiguous growth of the primary tumor, EOD Regional Nodes is used to code the regional lymph nodes involved, and EOD Mets is used to code the distant site or sites of involvement. Notes for site specific schemas take precedence over general guidelines.
The site-specific data item titled Microsatellite Instability is a useful prognostic marker in that the patients with high MSI colon cancers have a better response to surgery and survival. This happens when a change occurs in certain cells (such as cancer cells) in which the number of repeated DNA bases in a microsatellite is different from what it was when the microsatellite was inherited. Microsatellite instability may be caused by mistakes that don’t get corrected when DNA is copied in a cell.
