Clinicopathologic Features and the Loss of ARID1A Expression in Ovarian Seromucinous Borderline Tumors and Seromucinous Carcinomas.

The current study highlighted the ARID1A and SALL4 expression and described histopathologic and immunohistochemical features of ovarian seromucinous tumors (SMTs) including borderline tumors (SMBTs) and seromucinous carcinomas (SMC; namely as endometrioid carcinoma with mucinous differentiation according to WHO 2020 classification). The clinicopathological and immunohistochemical features of 38 SMTs were analyzed, including ARID1A, SALL4, estrogen receptor (ER), progesterone receptor (PR), TP53, keratin 7, keratin 20, CEA, CDX2, WT1, PAX2, and PAX8. SMCs and SMBTs comprised 68.4% (n = 26) and 31.6% (n = 12) of all SMTs, respectively, studied. The mean age of diagnosis was 47.4 years and 41.4 years, and the mean size was 9 cm and 7.45 cm for SMC and SMBT, respectively. There was endometriosis or endometriotic cyst in 61.5% of SMCs and 50% of SMBTs. Immunohistochemically, loss of ARID1A staining was observed in 15 (65.2%) of 26 SMCs, and 3 (33.3%) of the 12 SMBTs. Only one SMC showed focal SALL4 positivity. All SMTs were positive for ER, PR, PAX8, and keratin 7. SMTs were negative for WT1, keratin 20, CDX2, and CEA (negative in 66.7% to 92.3% of the cases). While all SMBTs and 24 (92.3%) of 26 SMCs exhibited "wild-type" TP53 staining, 2 (7.7%) SMCs, both were stage III, showed mutant type TP53 overexpression. We indicate there is a similarity between SMC and SMBT according to the immunohistochemical features. SMBTs are keratin 7, ER, PR positive tumors, and some of them have loss of ARID1A expression and are likely to develop in the background of endometriosis similar to SMC.