It is indistinct how clinically significant mismatch repair (MMR) status is in patients who are diagnosed with nonmetastatic cancer across tumor types. The study’s objective was to scrutinize the prognostic role that the lack of MMR plays in patients with stage I-III colorectal and endometrial disease.

The Hellenic Cooperative Oncology Group (HeCOG)’s tumor repository was used to find patients with nonmetastatic colorectal and endometrial cancer with tumor tissue that could be examined. The Departments of Medical Oncology, affiliated with HeCOG, referred patients through this. Immunohistochemistry was used to assess the MMR protein expression. The main outcome from this was overall survival (OS).

1158 patients (median age: 64 years, men: 544) with nonmetastatic colorectal (N=991) and endometrial cancer (N=167) were distinguished from May 1990 to September 2012. Adjuvant treatment was received by 109 (65%) patients with endometrial cancer and every patient who was diagnosed with colorectal cancer. A lack of MMR was detected in 114 (11.5%) colorectal tumors and 80 (47.9%) endometrial tumors. 69 (7%) patients were found to have a deficiency of the protein PMS2 while 63 (6.5%) patients with colorectal cancer had a deficiency of MLH1. In addition, 58 (34.7%) patients with endometrial cancer suffered from an MSH2 deficiency. There was a higher probability of colorectal tumors with a deficiency of MMR (dMMR) to be right-sided (65 % dMMR vs 27 % proficient MMR, pMMR; p < 0.001), high grade (31% vs 15%, χ2, p < 0.001) and with a mucinous component (64% vs 42%, p < 0.001). Usually, the endometrial dMMR tumors had endometrioid histology (51.4 % endometrioid vs 20 % serous/clear cell, p = 0.020). In comparison to the proficiency of MMR, the lack of MMR was related to an improvement in the overall survival of patients with endometrial cancer (HR = 0.38, 95% CI 0.20 to 0.76, p = 0.006). However, this was not the case for patients with colorectal cancer (HR = 0.73, 95% CI 0.49 to 1.09, p = 0.130). The positive prognostic importance of MMR deficiency in patients with endometrial cancer (HR = 0.42, 95% CI 0.20 to 0.88, p = 0.021) was kept up after adjustments were made for age, stage, and grade. Even though both patients with nonmetastatic endometrial cancer and nonmetastatic colorectal cancer received adjuvant chemotherapy, only the former had better outcomes from DMMR.