ESR1 and breast cancer: Since Caveolin1 plays a critical role in breast cancer, and its down regulation increases tumor aggressiveness [31], we first explore the profiles of CAV1 mRNA variants in breast cell lines, like MCF7, that are ERα++ HER2-/+ cancer cells; MCF10A, that are triple negative normal cells; MDA231, that are triple negative cancer cells and in human breast tumors samples negative for ERα according to Subik K. et al. 2010 [36].