ESR1 and breast cancer: Most breast cancer studies have focused on cadmium which induces the proliferation of estrogen-dependent breast cancer cells [144–147], increases the transcription and expression of estrogen-regulated genes such as the PR [144, 148], activates ERα in transfection assays [144–146, 149, 150], and increases signaling through the ERK1/2 and Akt pathways [148, 151, 152].