We then selected five breast cancer cell lines, including the triple-negative breast cancer (TNBC) cell lines MDA-MB-231 (MDA-231), BT549, and Hs578T, the luminal-type cell line T47D, and the HER2-positive cell line SK-BR-3, to investigate whether RACK1 regulates breast cancer cell proliferation. This evidence concerns the gene ERBB2 and triple-negative breast carcinoma.