NCT-58 is a potent inhibitor of C-terminal HSP90. NCT-58 does not induce the heat shock response (HSR) due to its targeting of the C-terminal region and elicits anti-tumor activity via the simultaneous downregulation of HER family members as well as inhibition of Akt phosphorylation. NCT-58 kills Trastuzumab-resistant breast cancer stem-like cells. NCT-58 induces apoptosis in HER2-positive breast cancer cells[1].