Reijnen C, Küsters-Vandevelde HVN, Ligtenberg MJL, et al. - In a large cohort classified as synchronous primary endometrial and ovarian cancers (SEOs) or metastatic disease, researchers examined the clonal link between endometrial and ovarian carcinomas. To determine the primary origin, they performed a comparison of molecular profiles with The Cancer Genome Atlas (TCGA) data. They found that at least one somatic mutation was shared by endometrial and concurrent ovarian carcinoma in 92% of SEOs (46/50), with a clonality index above 0.95, this supports a clonal origin. Remarkable similarities with the TCGA endometrial carcinoma set were demonstrated by SEO molecular profiles. Poor clinical outcome was independently predicted by TP53 mutations and extra-utero-ovarian disease. In an overwhelming majority of cases, the SEOs were found to be clonally related. A favorable prognosis was displayed by SEOs. The molecular profiles of SEOs indicated a primary endometrial origin. Adjuvant systemic treatment planning may be influenced by TP53 mutation and extra-utero-ovarian disease.