ERBB2 and breast cancer: Since ganetespib-mediated effects on apoptosis in ErbB2+ breast cancer cells have not been well-documented, we treated BT474 and SKBR3 cells with ganetespib (0-250 nM) for 16 hours, followed by Annexin V and propidium iodide (PI) staining to examine the effects of ganetespib on apoptosis.