ERBB2 and breast cancer: In addition to these findings, we found that a higher risk of recurrence in HER2+ and HER2-/ER+ breast cancer subtypes was significantly correlated with increased expression of HSP90AA1 and HSP90B1; and increasing expression of HSP90AA1 and HSP90AB1 were significantly associated with a higher chance of distant metastasis in patients with HER2-/ER+ tumor (Additional file 7).