Objectives Identification of DNA mismatch repair (MMR) deficiency has been proposed as a screening strategy for Lynch Syndrome (LS) in endometrial cancer (EC) patients and is useful in predicting tumor sensitivity for immune checkpoint blockade therapies. The proportion of EC with MMR deficiency is reported to be 26%, and around 3% of EC may be attributed to LS. The present study aims to identify clinicopathological features of EC patients tested for tumoral MMR expression in a Brazilian cancer center.

Methods 479 patients treated for EC from 2010 through 2020 at Instituto do Câncer do Estado de São Paulo (ICESP) had their tumors analyzed by immunohistochemistry for MLH-1, MSH-2, MSH-6 and PMS-2. Clinical and pathological information from these cases were retrieved using a REDCap database and statistics were calculated using the SPSS software.

Results From the 479 cases analyzed, 453 resulted in conclusive immunostainings for MMR enzymes: 305 (67%) were MMR proficient (pMMR) and 148 (33%) were MMR deficient (dMMR). Results comparing the two groups are shown in table 1.

Conclusions In this population, dMMR EC had a higher prevalence than previously reported. Detection of germline mutation is necessary to investigate whether LS is more prevalent. Clinical aspects did not differ between groups. Lymphvascular space invasion was more frequent in the tumors of the dMMR group, whereas aberrant p53 immunostaining was more prevalent in the pMMR group. Mortality was significantly higher in the dMMR group.