ERBB2 and breast cancer: NARF expression was induced by hypoxia in all breast cancer cell lines analyzed, including hormone (estrogen and/or progesterone) receptor-positive (HR+) MCF-7 and T47D cells, HER2+ HCC1954 cells, and triple-negative (HR− and HER2−) MDA-MB-231, SUM149, and SUM159 cells.62 Knockdown experiments in HR+ MCF-7 and HR− MDA-MB-231 cells revealed that hypoxia-induced NARF expression was dependent on HIF-1α and independent of HIF-2α.