ERBB2 and cancer: Moreover, certain malignant growth-related proteins (e.g. Raf-1, ErbB2, Akt, HIF-1α, and others) are clients of the Hsp90 chaperone and may undergo proteasomal degradation in cancer cells treated with the Hsp90 activity inhibitors [6,8,10]; if so, the expression levels of these proteins may become down-regulated and such signs may be detectable as indicators of the Hsp90 dysfunction.