Microsatellite instability status does not predict total lymph node or negative lymph node retrieval in stage III colon cancer.

The relationship between higher total lymph node resection number in colorectal cancer resection specimens and improved overall survival is well known. Recent studies describe an association between a high rate of microsatellite instability and a high total lymph node count in colorectal cancer. Higher lymph node retrieval may potentially explain the improved survival seen in cancers with microsatellite instability. We investigate whether these associations can be validated in a cohort of American Joint Committee on Cancer stage III colon cancers. Medical records from 200 cases of stage III colon cancer resection specimens were reviewed, and sufficient tissue was available for 168. Expression of DNA mismatch repair proteins was determined by immunohistochemistry, and microsatellite status, by polymerase chain reaction. The mean total lymph node count in cases with microsatellite instability versus microsatellite stable tumors (15.9 versus 16.9; P = .664) and the mean number of negative lymph nodes in each respective category (12.2 versus 13.6; P = .522) were not significantly different. There was no difference between microsatellite stable cases and cases with microsatellite instability when total lymph node counts (P = .953) or negative lymph node counts (P = .381) were analyzed with respect to percentage of cases above and below the medians. This cohort of stage III colon cancers does not support a significant relationship between microsatellite status and a higher retrieval of total or negative lymph nodes. Although microsatellite instability is associated with improved overall survival in our cohort (P = .026), the reason for this does not appear to be related to higher numbers of retrieved lymph nodes.