Expression analysis of cystatin C and M in laser-capture microdissectioned human breast cancer cells--a preliminary study.

Cathepsins B and L, implicated in the progression of malignant tumors, are regulated by a family of endogenous inhibitors referred to as the cystatins. Cystatin M was identified by differential display as down-regulated gene in metastatic breast cancer cells. However, this finding has yet to be confirmed in clinical breast cancer specimens. Our objective is to examine the expression levels of cystatins C, M, and cathepsins B and L mRNA in breast cancer cells isolated by laser capture microdissection. The mRNA and protein levels of cathepsin B, L, and cystatin C and M in breast cancer specimens were determined utilizing laser capture microdissection/RT-PCR, Western blotting, and immunohistochemical methods. Expression levels of either cystatin M or C were not significantly different between lymph node-positive and -negative breast carcinomas. Increased expression levels of both cystatin M and C correlated significantly with larger tumor size. Cystatin M mRNA was detected by in situ hybridization in both primary and metastatic breast cancer cells. Our findings are at variance with a previous report proposing a metastasis suppressive function for cystatin M. Therefore, additional studies in a larger series with adequate follow-up are necessary to elucidate the biologic significance of cystatin M expression in breast cancer metastasis.