These data demonstrate that leptin favors cancer cell aggressiveness and, since leptin did not increase pAKT and pJAK in all cancer cell lines (Supplementary Fig. S2), increased ERK activation in all cell lines and only increased proliferation in ER+/PR+ cells, it suggests an alternative mechanism to the ERK pathway by which leptin increases proliferation in hormone receptor-positive cells and not triple-negative breast cancer cells. This evidence concerns the gene ESR1 and cancer.