S5-1: Neoadjuvant Pertuzumab (P) and Trastuzumab (H): Biomarker Analyses of a 4-Arm Randomized Phase II Study (NeoSphere) in Patients (pts) with HER2−Positive Breast Cancer (BC)

Background: NeoSphere showed that P with H and docetaxel (T) had a significantly higher pCR rate (45.8%) compared with TH (29%) or other P combinations (HP, TP) (Gianni, SABCS 2010). HER2+/ER+ and HER2+/ER− BC have different patterns of gene expression, and treatment response seems to be driven by different biologic pathways (Bianchini, ASCO 2011). This effect was also seen in NeoSphere. A broad panel of biomarkers (BMs) was assessed in tumor specimens and in sera to characterize the molecular profile of the ITT population and to explore BMs with different treatments and in different subsets of pts. Methods: Core biopsies and sera from 387/417 pts collected at baseline were available for BM analyses. HER2, all its truncated forms, HER3, IGF1R, PTEN, and pAKT were assessed by IHC and a modified H-score was derived per each marker. HER1, HER2, HER3, amphiregulin (AREG) and betacellulin mRNA expression in tumor tissue was assessed by qRT-PCR. C-myc was assessed by FISH. Mutational analyses of 8 hot spots within PIK3CA on tumor DNA was done via TaqMan-PCR. ELISA was used to detect HER2 extracellular domain (ECD), AREG, EGF, and TGFα in serum. Treatment interaction test was performed to test for association between BMs and pCR. In the analysis, median values were used as cutoffs, except for PTEN, PIK3CA mutation, and c-myc amplification, where cutoffs were applied following a biologic rationale. Results: In the overall population, high HER2 membrane protein expression measured by modified H-score was associated with a significantly higher pCR rate in the THP arm (p=0.001), with a large benefit from combination of P with TH (OR=3.74, CI 80%, 2.21−6.34; p=0.0009). The cutoff derived from NeoSphere has no immediate clinical applicability. A decreased likelihood of pCR was detected for pts with PI3K mutations in all 4 arms in a preliminary analysis limited to about 70% of cases. A final analysis will be presented. A significantly different distribution of BM expression in the ER+ vs ER− subgroups was found for 10 of 16 BMs (FDR Summary: The level of HER2 membrane protein expression was associated with increased benefit from combination of P with TH. The PI3K mutational status appears to have a relevant role in defining the likelihood of response with all treatments. The different treatment effects according to ER status are reflected in a different molecular BM profile in ER+ vs ER− tumors, with the IGF1R membrane score being correlated with ER− tumors. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S5-1.