We next compared the endogenous expression levels of ID2 and TFCP2L1 in human BC cells derived from muscle-invasive BC (MIBC) tumors with different molecular classifications, including basal-like subtype (5637 and HT1197), luminal-like subtype (HT1376)13,23, and mixed subtype (T24 and UMUC3) cells, as well as in the RT4 cell line, often used as a model of non-muscle-invasive BC24. The gene discussed is ID2; the disease is breast cancer.