Elevated WBP2 Expression in HER2-positive Breast Cancers Correlates with Sensitivity to Trastuzumab-based Neoadjuvant Therapy: A Retrospective and Multicentric Study

Purpose: Trastuzumab-based chemotherapy has shown remarkable clinical benefits for patients with HER2-positive breast cancer. However, treatment regimens involving trastuzumab had little or no effect for a subset of patients. Preliminary studies revealed WW-binding protein 2 (WBP2), an oncogenic transcription coactivator, to be coamplified with HER2 in 36% of HER2-positive breast cancers. We hypothesize that WBP2 regulates and correlates with the response of HER2-positive breast cancer to trastuzumab.

Experimental Design: The coexpression of WBP2 and HER2 in breast tumors was validated using IHC. The role and mechanism of WBP2 in regulating breast cancer response to trastuzumab was elucidated using , patient-derived xenograft and murine xenograft models. A multicenter retrospective study involving 143 patients given neoadjuvant trastuzumab-based chemotherapy was conducted to determine whether WBP2 expression correlates with pathologic complete response (pCR).

Results: Elevated expression of WBP2 significantly enhanced breast cancer's response to trastuzumab by augmenting trastuzumab-induced HER2 downregulation and cell-cycle arrest via inhibition of cyclin D expression. High level of WBP2 correlated with better pCR (67.19%) compared with low WBP2 level (26.58%). The highest response was observed in subgroups of patients with high WBP2-expressing tumors also aged below 50 years (77.78%) or were premenopausal in status (73.33%). Retrospectively, WBP2 demonstrated sensitivity of 80% to 81% and specificity of 76.5% to 80% in discriminating between patients showing pCR and non-pCR.

Conclusions: WBP2 expression correlates with the response of HER2-positive breast cancer to trastuzumab-based neoadjuvant chemotherapy.