ERBB2 and neoplasm: In mouse and human models of ErbB2+ breast cancer, ErbB2 overexpression was shown to activate heat shock factor-1 (HSF1), a master transcription factor required for HSP90 synthesis, and stabilize various tumor-promoting HSP90 clients, including macrophage-migration inhibitory factor (MIF)14, Akt, EGFR, ErbB2, c-Raf, and mutated p5315.