The need for valid in vivo models for further testing Hsp90-targeted cancer therapy, currently under clinical trial with promising early results [22,51-53], also appears to be essential, as a recent study has highlighted a potential contraindication to this therapy, since the Hsp90 inhibitor, 17-allylamino-17-demothoxygeldanamicin (17-AAG), appears to enhance bone metastasis of a human breast cancer cell line following intracardiac inoculation in the nude mouse [54]. This evidence concerns the gene HSP90AB1 and breast cancer.