To validate these findings, a panel of samples including normal breast cells, breast cancer cell lines (including ESR1+ cell lines, estrogen nonresponsive cell lines, ERBB2 over-expressing cell lines and 55 primary tumour samples, some of which had been depleted of F19-expressing fibroblasts) were analysed by semi-quantitative RT-PCR for RGS2 expression. Here, ERBB2 is linked to breast cancer.