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. This evidence concerns the gene LAMA4 and breast carcinoma.