Furthermore and taking into account previously reported data showing that mAb 4C5 inhibits cancer cell invasion by disrupting association of extracellular HSP90 with HER2 [28] and metalloproteinases MMP2 and MMP9 [29] in this work we investigate the possible effect of this cell impermeable anti-HSP90 antibody on the interactions of surface Cdc37 with HSP90 and the ErbB receptors. This evidence concerns the gene CDC37 and cancer.