Much higher protein levels of caveolin-1 were also observed in the highly invasive ERα-negative MDA-MB-231 and Hs578T cells when compared to the non-metastatic ERα-positive MCF-7 and T47D cells, indicating a strong correlation between caveolin-1 expression and breast cancer aggressiveness (Supplementary Fig. S6). This evidence concerns the gene ESR1 and breast cancer.