Mutation profile and clinical outcome of mixed endometrioid-serous endometrial carcinomas are different from that of pure endometrioid or serous carcinomas.

Clinical outcome of 23 patients with mixed endometrioid and serous endometrial carcinomas (mixed EEC-SC) was compared to that of pure endometrioid (EEC) and pure serous (SC) carcinomas. Hotspot mutation frequencies in KRAS, PIK3CA, PTEN, and TP53 and microsatellite instability (MSI) status were determined in mixed EEC-SC, as well as in their EEC and SC microdissected components separately, and alterations were compared to frequencies in pure EEC and SC. Relapse-free (RFS) and overall survival (OS) differed significantly between mixed EEC-SC and pure EEC and SC, revealing that outcome of mixed EEC-SCs was intermediate to that of pure EEC and pure SC. PTEN mutations were absent in pure SC, but occurred in 20 % of pure EEC, and 13 % of mixed EEC-SC. In contrast, TP53 mutations were more frequent in pure SC (17 %) and mixed EEC-SC (22 %) than in pure EEC (2 %). Mutations in mixed EEC-SC were shared by the two microdissected components in 30 %, whereas in 35 %, some mutations were component-specific. Mutation analysis confirms similarities between the EEC and SC components of mixed EEC-SC with pure EEC and pure SC, respectively. However, PTEN and KRAS mutations were more frequent in the SC component of mixed EEC-SC than in pure SC, while TP53 mutations were more frequent in the EEC component of mixed EEC-SC than in pure EEC. Presence of different clonal mutation pattern between EEC and SC components of mixed EEC-SC raises the possibility of divergent tumor heterogeneity or biclonal origin in some cases.