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 a nd is usually interpreted as a result of a field defect. Sporadic synchrono us 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 p resent a diagnostic dilemma. Two cases of synchronous adenocarcinomas of th e endometrium and colon were studied for genetic abnormalities and differen ces to test for the presence of two primary tumors. Primary tumors, metasta ses, and normal tissues were microdissected from formalin-fixed, paraffin-e mbedded tissues. PCR amplification was performed for microsatellite DNA mar kers on chromosome 17q and 11q13. The colonic tumors were moderately and po orly differentiated, invasive, nonmucinous adenocarcinomas, whereas one ute rine tumor was endometrioid adenocarcinoma and the other was papillary sero us 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 dif fered between the two primary tumor sites. Moreover, the lymph node metasta sis in one colonic tumor had genetic alterations that differed from that of the primary tumor. In both patients, the molecular studies suggested the p resence 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 fro m the primary tumors and associated metastases.