The composition of proteoglycans and their changes during malignant transformation are important factors influencing adhesive properties and mitotic activity of tumor cells. In this study, expression level of different proteoglycans (decorin, syndecan-1, lumican, glypican-1, and aggrecan) in tumors and normal human breast tissue was investigated. Multiplex RT-PCR data revealed different expression changes for different proteoglycans in human breast tumors--syndecan expression was activated compared to almost no expression in normal breast tissue, expression of decorin and lumican decreased 2-5- and 2-3-fold, respectively, and aggrecan transcription seems to be unaffected. A change of expression level of decorin correlated with expression of D-glucuronyl-C5-epimerase, a key enzyme responsible for the biosynthesis of idurone-containing glycosaminoglycans, possessing antimitotic activity. The results suggest that changes in decorin, lumican, and syndecan-1 expression in tumor tissue could induce a distortion of proteoglycan composition and mitotic activity of cells in human breast tumor.