To study the function of miR-208a in breast tumors, we first detected the endogenous level of miR-208a in multiple breast cancer cell lines, and found lower miR-208a expression in estrogen receptor positive ZR75–1 and triple negative MDA-MB-231 (MM-231) cells, compared to other breast cancer cell lines (Fig. 3A). The gene discussed is ESR1; the disease is breast neoplasm.