According to a classification of endometrial carcinomas based upon mutations in nine genes, including ARID1A, PTEN, PIK3CA, KRAS, P53, and BRAF, the rate of ARID1A mutation in low−grade endometrioid adenocarcinomas is 47%, while in high−grade endometrioid adenocarcinomas, serous adenocarcinomas, and carcinosarcomas, it is 60%, 11%, and 24%, respectively (23). Here, ARID1A is linked to carcinosarcoma.