Abstract: BACKGROUND ＆ AIM: To explore the expression of cystatin M, a major cysteine protease inhibitor, in human breast cancer and its significance. MATERIAL AND METHODS: A semi-quantitative reverse transcription polymerase chain reaction and immunohistochemical methods were performed to evaluate the expression of cystatin M in cancerous and noncancerous tissues of fifty pairs of human invasive ductal adenocarcinoma of breast. The relationship between the expression of cystatin M gene in human breast carcinoma and clinilcopathological features was analyzed. RESULTS: Reduced expression level of cystatin M gene mRNA and protein has been noted in breast carcinoma cells compared to adjacent noncancerous breast tissue (P<0.01). The lower experssion levels in breast carcinoma cells was related with clinicopathological features including lymph-node metastasis and TNM staging (P<0.05) but not with the histological grade nor the estrogen and progesterone receptor status (P>0.05). CONCLUSION: The expression of cystatin M gene mRNA and protein was reduced in human invasive breast carcinoma. Down-regulated expression of cystatin M in breast carcinoma might be associated with tumor invasion and metastasis.

Key words: breast carcinoma, cystatin M gene, gene expression, metastasis