245P Clinicopathological Features Including Response to Platinum-Based Chemotherapy in Endometrial Carcinomas Involving SWI/SNF Complex Inactivation

Dedifferentiated endometrial carcinoma (DDEC) and undifferentiated endometrial carcinoma (UDEC) are uncommon but exhibit aggressive clinical courses. Recent studies reported the loss of expression of SMARCB1 (INI1), SMARCA4 (BRG1), or ARID1A and ARID1B, core or DNA-binding subunits of switch/sucrose non-fermenting (SWI/SNF) complex, resulted in inactivation of SWI/SNF complex that was related to dedifferentiation of endometrial carcinoma. The efficacy of platinum-based chemotherapy that is standard care for differentiated endometrial carcinoma is still unknown for UDEC and DDEC. Thirteen patients diagnosed with UDEC or DDEC at our institute between 1999 and 2019 were included in this retrospective study. Inactivation of SWI/SNF complex was defined as deficiencies in expression of either INI1, BRG1, or ARID1A and ARID1B. Mismatch repair (MMR) status was also confirmed by immunohistochemistry. We evaluated clinical features and outcome in UDEC and DDEC. The median age at diagnosis was 54 years (range, 47-61). 2/5/6 patients presented with stage I/III/IV disease, respectively. Loss of INI1/BRG1/ARID1A and ARID1B was observed in 1/5/8 patients. Of the 11 patients whose MMR status were evaluated, 9 (82%) were identified as MMR deficient. Two patients underwent surgery alone because of early stage. Three patients received platinum-based chemotherapy as adjuvant therapy, and none of them has relapsed. Of the 8 patients who were unresectable or incompletely resected, 3 patients received platinum-based chemotherapy (doxorubicin/cisplatin or paclitaxel/carboplatin), 4 patients did not due to poor PS, and 1 patient did other regimen. In patients with unresectable or incompletely resected disease with platinum-based chemotherapy, response rate (RR), median progression free survival, and median overall survival (mOS) were 100%, 9.1 months, and 18.6 months, respectively. In patients with unresectable or incompletely resected disease without platinum-based chemotherapy, mOS was 2.7 months. Platinum-based chemotherapy showed high RR for UDEC and DDEC. We will report case presentation about a few cases with specific clinical courses.