Clinicopathological and Survival Characteristics of Mismatch Repair Status and PD-1 Expression in Serous Ovarian Cancer.

ABSTRACT

OBJECTIVE: To evaluate the clinicopathological characteristics of mismatch repair (MMR) deficiency and its clinical outcomes by performing immunohistochemistry (IHC) for MMR genes in the serous ovarian cancer (SOC) tumour sections. STUDY DESIGN: A retrospective case-control study. Place and Duration of the Study Gynecology Department of Kanuni Sultan Süleyman Training and Research Hospital, and Department of Medical Oncology of Medipol University, between March 2001 and January 2020. METHODOLOGY: IHC was carried out for MLH1, MSH2, MSH6, and PMS2 on full-section slides from 127 SOCs to evaluate the MMR status. MMR-negative and MMR-low groups together were defined as MMR deficient and called microsatellite instability-high (MSI-H). The MSI status and expression of programmed cell death-1 (PD-1) were compared in SOCs with different MMR statuses. RESULTS: A significantly higher frequency of MMR-deficient SOCs was diagnosed at early stages compared with the patients in the MSS group (38.6% and 20.6%, respectively, p=0.022). The frequency of cases with PD-1 expression was significantly higher in the MSI-H group (76.2%) than in the MSS counterparts (58.8%, p=0.028). Patients in the MSI-H group had significantly longer DFS (25.6 months) and OS (not reached) than those in the MSS group (16 months and 48.9 months, p=0.039 and p=0.026, respectively). CONCLUSION: MSI-H SOCs were diagnosed at an earlier stage as compared to MMR proficient cases. The presence of PD-1 expression was significantly higher in cases presenting MMR deficiency compared with MMR-proficient cases. MSI status was significantly associated with DFS and OS. KEY WORDS Serous ovarian cancer, Microsatellite instability, Mismatch repair deficiency.