Mechanistically, HER3 activation suppresses the tumor-suppressive microRNA miR-34b-5p, resulting in the upregulation of the histone demethylase PHF8 (KDM7B), which in turn represses the expression of the CDK inhibitor p27Kip1 and facilitates G1–S cell cycle progression. The gene discussed is ERBB3; the disease is neoplasm.