Abstract P3-06-04: Role of pMAPkinase, pAKT, p27 & IGF-IR as predictive markers of response to trastuzumab in patients with HER2-positive invasive breast cancer treated with neoadjuvant chemotherapy + trastuzumab in the REMAGUS02 trial

Background: Predicting a benefit from trastuzumab in patients with HER2+ breast cancer remains an important goal. Possible mechanisms of resistance include altered receptor antibody interaction, Akt and MAPK pathways, and loss of p27. The objective of this study was to determine the correlation between pMAPkinase (pMAPK), pAKT, p27, IGF-IR protein expression and the benefit of trastuzumab for patients randomized to chemotherapy (CT) alone and CT with trastuzumab. Patients and methods: From May 2004 to October 2007, 120 patients with stage II and III HER2+ breast carcinomas were enrolled in a phase II trial of neoadjuvant chemotherapy (CT) with epirubicin-cyclophosphamide (4 courses) followed by docetaxel ± trastuzumab (T) (4 courses). A complete pathological response (pCR) was defined by the absence of residual invasive carcinoma in the breast and axillary lymph nodes. A tissue microarray was constructed from paraffin-embedded tumor samples collected prior to neoadjuvant chemotherapy. Patients9 tumours were scored HER2 3+ immunohistochemically (IHC) or 2+ IHC with HER2 amplification by FISH. Immunohistochemical analysis of pMAPK, pAKT, p27 and IGF-IR was performed on tumor tissue microarrays before CT. The H-score (intensity × %) was evaluated. Specimens were classified as exhibiting high or low expression based on a median value as the cut-off point for each marker. A logistic regression model, including the marker and its interaction with treatment, was used to analyse the markers predictive of a treatment effect on the pCR. The independent predictive value was analysed in a multivariate logistic regression adjusting on the lymph node and ER status. Results: 117/120 (97.5%) patients had sufficient tumor for the analysis. The pCR rate was 19% in the CT arm and 25% in the CT+T arm. The median H-score was: pMAPK = 28, pAKT= 25, p27= 50 and IGF-IR = 15. No significant difference was observed in the pCR rate between the two arms according to pAKT, p27, IGF-IR expression. The pCR rate was higher in CT+T compared to CT alone in patients with high pMAPK expression (OR = 4.7 (0.9–24.2); interaction p = 0.03). No difference was observed in the pCR rate in patients with low pMAPK expression (OR = 0.5 (0.1–1.8). Conclusions: In HER2-positive breast cancers, pMAPK expression evaluated by IHC was significantly associated with a pathological response in the arm with neoadjuvant trastuzumab. High pMAPK expression could be a predictive marker of response to trastuzumab in a CT +T regimen. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-06-04.