We showed that exposure of human breast stromal fibroblasts to the soluble factors secreted by five human breast cancer cell lines of distinct molecular profile and degree of invasiveness (i.e., MCF-7, SKBR3, ZR-75-1, MDA-MB-231 and MDA-MB-468 [109,110]) resulted in decorin down-regulation in young and senescent cells. The gene discussed is DCN; the disease is breast cancer.