Simultaneous carcinomas of the endometrium and ovary may represent a diagnostic dilemma and the clinical management of such cases may be problematic. In surgical pathology practice, we classify them either as double primary tumors (DP) or a single primary tumor with metastasis (PM), according to the conventional clinicopathologic criteria. The distinction has important therapeutic and prognostic implications, but it can be sometimes difficult, especially in advanced cases. In this study, in addition to the clinicopatho-logic classification, we assessed tumor cell clonality in 13 cases with synchronous endometrial and ovarian endometrioid adenocarcinomas using PCR-based microsatellite analysis of microdissected archival tissues for loss of heterozygosity (LOH) and microsatellite instability (MSI). All paired endometrial and ovarian tumors demonstrated either MSI or/and LOH except for 1 case, and therefore the microsatellite analysis was informative in 92.3% of the cases. Nine of 26 tumors (34.6%) exhibited MSI-H and 15 of 26 (57.7%) showed LOH. In contrast to 4 DP cases and 9 PM cases classified according to clinicopathologic criteria, microsatellite analysis suggested 10 DP cases and 2 PM cases. The molecular analysis was not informative in 1 case. Thus, analysis of microsatellite abnormality is a helpful adjunct in the assessment of synchronous tumors, especially to differentiate DP from PM cases in advanced tumor cases. Moreover, the combination of conventional clinicopathologic evaluation and molecular analysis is important and helpful in distinction between the two groups of synchronous tumors.

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