Higher frequency of isolated PMS2 loss in colorectal tumors in Colombian population: preliminary results

Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of death worldwide. It accounts for >9% of all cancers. One of the pathogenic factors of CRC is germline mutation, leading to alteration and inactivation in the mismatch repair (MMR) genes. The aim of the study is to compare the frequency of alterations in MMR protein expression in Caucasian CRC patients with Colombian CRC patients. A total of 45 Colombians and 48 Caucasians with CRC were studied. The microsatellite instability status of tumors was determined in primary CRC by immunohistochemistry using the automated Ventana Ultra. The combined loss of MLH1 and PMS2 was the most common alteration in both Colombian (11%, five out of 45) and Caucasian (12%, six out of 48) CRC patients. Interestingly, the loss of PMS2 expression in the presence of intact MLH1 was the second most common alteration in Colombians (8%, four out of 45), which was never seen in the Caucasian cohort (P=0.05). The loss of MLH1 alone and the combined loss of MSH6 and PMS2 expression were only observed in one out of 45 (2%) Colombians but not in Caucasians. The combined loss of MSH2 and MSH6 was not observed in any of the patients studied. The preliminary findings support a significant difference in alterations of MMR protein expression in Colombian CRC patients compared with Caucasian CRC patients. These findings are novel and warrant further studies in larger cohorts.