OBJECTIVETo investigate the incidence and clinicopathologic significance of MSI and LOH on 3P in breast carcinoma and its precancerous lesions, intraductal papillary adenoma and ductal carcinoma in situ.

METHODS41 paired sporadic invasive breast carcinomas, 13 archival precancerous lesion specimens of the breast and 14 couples of benign hyperplasia were collected. Twelve microsatellites on chromosomes 2p, 3p, 5q, 6q, 16q, 17q, eleven markers on chromosome 3p were amplified for MSI and LOH, respectively, by polymerase chain reaction ( PCR ) with designed primers and detecting after polyacrylamide gel electrophoresis. In addition, the expression of protein of hMSH2, hMLHI, FHIT, ER, and PR were detected by immunohistochemistry.

RESULTSMSI was observed, at least two microsatellite markers, in 15 out of 41 (36. 6%) of the carcinomas, almost all belonging to poorly or intermediately differentiated carcinoma. Instability was shown in 9 of the 13 cases of precancerous lesions, but only 2 among them had more than 2 MSI sites. There was no MSI in benign hyperplasia. MSI was targeted predominately at D3S1766, D2S2739 in both carcinomas and precancerous lesions. Of the 11 loci examined, D3S1295, D3S1029 and D3S1038 were identified as the locus with most frequent LOH which were all correlated significantly with some clinicopathological parameters such as histological type, lymph node metastasis in breast cancer, while D3S1295 and D3S1029 were the most frequent markers in precancerous lesions. LOH of D3S1295 had significant correlation with negative expression of FHIT. Positive expression of hMLH1 and hMSH2 protein was detected in breast carcinomas in scattered distribution and their positive rate was 45% and 40% , respectively. In precancerous lesions, hMLH1 and hMSH2 protein showed diffuse expression and their positive rate was 61. 54% and 76. 92% , respectively, significantly lower than that in the control tissues.

CONCLUSIONDefective expression of MMR genes is closely associated with the development of breast cancer. Genomic instability might play a role in the early stage during multi-step mammary carcinogenesis. MSI indicates poor histological differentiation in breast carcinoma. D3S1766 and D2S2739 might be the sensitive sites to detect MSI in breast carcinoma and precancerous lesions. The smallest common LOH deletion regions seem likely to be situated between 3p14 and 3p25, indicating the existence of breast tumor related genes in those regions and some of them might affect tumor development.