piR-2158 suppressed cell proliferation, migration, EMT and stemness in human breast cancer. In order to determine the function of piR-2158 in breast cancer, a triple-negative breast cancer cell line MDA-MB-231 and luminal breast cancer cell line MCF-7 were transfected with piR-2158 or anti-piR-2158, respectively, followed by a series of functional assays including cell proliferation, migration, invasion, EMT and CSC analysis. The gene discussed is PIR; the disease is triple-negative breast carcinoma.