Evaluation of immunohistochemical expression of mismatch repair proteins in endometrioid and seromucinous borderline ovarian tumors a 10-year experience in a large health care institution.

e17557 Background: Borderline tumors (BT) are atypical proliferation of epithelium in the ovary in the absence of destructive stromal invasion, representing for 15% of all epithelial ovarian cancers. [1] Around 10% of the ovarian tumors are hereditary, and approximately 10% of all the hereditary forms of epithelial ovarian tumors are result of a loss of DNA mismatch repair (MMR). [2] Endometrioid borderline tumor (EBT) and Seromucinous borderline tumors (SMBT) are rare tumors in ovary and there is limited literature available on immunohistochemical (IHC) expression of Mismatch repair proteins(MMRP)in these tumors.[3, 4] The aim of this study is to evaluate IHC expression of MMRP in EBT and SMBT of ovary. Methods: Pathology database was searched for ovarian Endometrioid borderline tumor (EBT) and Seromucinous borderline tumor (SMBT) for a 10-year period (2010-2020). The cohort consisted of 10 EBT (6 of which had focal microinvasion or carcinoma) and 12 SMBT(2 of which had focal carcinoma ). For comparison, 1 borderline Brenner. 15 serous borderline tumors (SBT) and 15 mucinous borderline tumors (MBT) were also included. After reviewing slides, a block with adequate borderline tumor was selected for IHC stains. For the cases with carcinoma, two different blocks with each component were selected. In all selected blocks, IHC stains for four MMRP (MLH1, PMS2, MSH2, MSH6) were performed. The complete absence of nuclear staining in tumor cells was considered as “loss” of the MMRP expression. Any “weak” or “focal” nuclear staining was considered intact. Results: Total 53 cases were evaluated for MMRP IHC. All cases had intact MMRP expression. In cases with carcinoma, both components (BT and carcinoma) have intact MMR IHC expression. See table. Conclusions: Our study did not show loss of MMRP IHC expression in EMT or SMBT. However, our study consisted of a small number of cases. Multi Institutional study with a large number of cases can be helpful in future to further evaluate the role of MMRP IHC in EMT and SMBT. [Table: see text]