Based on the high frequency of ER-positive tumors in the ECM3 cluster and on the known TGFβ induction of ECM genes in fibroblasts [36]; [37], we carried out qPCR analysis of 6 representative ECM3 genes (COL1A1, COL5A2, SPARC, LAMA4, COL6A3 and MMP11) in ER-positive (ZR75.1 and BT474) and -negative (MDAMB231) breast carcinoma cell lines as well as on GM847 fibroblasts to investigate possible pathways involved in ECM3 gene expression in tumor cells. The gene discussed is SPARC; the disease is breast carcinoma.