The use of microsatellite instability in the distinction between synchronous endometrial and colonic adenocarcinomas

The association of endometrial carcinoma with other gynecologic neoplasms, especially ovarian and fallopian tube carcinoma, has been well documented and is usually interpreted as a result of a field defect. Sporadic synchronous primary carcinomas occurring in the endometrium and colon are extremely rare, especially in the absence of the familial genetic abnormalities seen in hereditary nonpolyposis colorectal carcinoma (HNPCC) syndrome, and may present a diagnostic dilemma. Two cases of synchronous adenocarcinomas of the endometrium and colon were studied for genetic abnormalities and differences to test for the presence of two primary tumors. Primary tumors, metastases, and normal tissues were microdissected from formalin-fixed, paraffin-embedded tissues. PCR amplification was performed for microsatellite DNA markers on chromosome 17q and 11q13. The colonic tumors were moderately and poorly differentiated, invasive, nonmucinous adenocarcinomas, whereas one uterine tumor was endometrioid adenocarcinoma and the other was papillary serous carcinoma. Although microsatellite instability, as evidenced by changes in the lengths of the amplified PCR products, was detected at 17q and 11q13 loci in the uterine and colonic neoplasms, the patterns of instability differed between the two primary tumor sites. Moreover, the lymph node metastasis in one colonic tumor had genetic alterations that differed from that of the primary tumor. In both patients, the molecular studies suggested the presence of two synchronous primary tumors. Molecular techniques may assist in distinguishing two separate primaries by determining the contraction and expansion of microsatellite regions in DNA obtained by microdissection from the primary tumors and associated metastases.