Synchronous development of carcinomas in the endometrium and ovaries is a fairly common phenomenon, but distinction of a single clonal tumor with metastasis from 2 independent primary tumors may present diagnostic problems. To determine clonality and the occurrence of progression, we microdissected multiple foci from 17 cases of synchronous endometrioid carcinomas and studied loss of heterozygosity (LOH), microsatellite instability (MI), and PTEN mutations. In 14 of the 17 cases, genetic alterations were either homogeneous or found in only some of the foci. LOH was detected for 10q (4 cases), 17p (2 cases), and 2p, 5q, 6q, 9p, 11q, 13q, and 16q (1 case each). Four cases had the MI phenotype with discordant MI patterns between both tumor sites, thus indicating a biclonal or triple clonal process. In 3 of 6 cases with PTEN mutations, identical mutations in both tumor sites indicated a single clonal neoplasm. Altogether, 14 synchronous tumors were genetically diagnosed as follows: single clonal tumor, characterized by concordant genetic alterations in both tumor sites, including identical LOH, identical PTEN mutations, and/or identical sporadic allelic instability patterns (4 cases); single clonal tumor with genetic progression, homogeneous LOH or identical PTEN mutations in both tumor sites and progressive LOH in ovarian metastatic foci (2 cases); and double (7 cases) or triple clonal tumors (1 case), determined by discordant PTEN mutations, heterogeneous LOH, and/or discordant MI patterns. Thus, 35% of synchronous tumors were monoclonal, 47% were polyclonal, and 18% were undetermined. The favorable prognosis of synchronous endometrioid carcinomas may be due to the occurrence of PTEN mutations in both independent and metastatic tumors, the MI-positive independent primary tumors, and the low frequency of LOH.
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