In 2009 a prospective, randomized Phase II trial (NCT00842998) was initiated to evaluate the activity of HER2-targeting agents without
chemotherapy (CT) in HER2-positive metastatic
breast cancer (MBC) patients. The primary
tumors of the patients enrolled in this study offered a unique opportunity to identify
biomarkers that could predict durable clinical benefit from CT-free anti-HER2
therapy. Patients with HER2-positive MBC were randomized to
trastuzumab or
lapatinib as first-line
therapy. CT was added to anti-HER2
therapy in patients failing to achieve
tumor regression at the 8-week evaluation and in those progressing at any time. Expression analysis of 105 selected genes was performed from
formalin-fixed
paraffin-embedded primary
tumor samples. The research-based PAM50 intrinsic subtypes were also identified. Additionally, quantitative HER2 (H2T) and p95HER2 (p95)
protein expression were evaluated by HERmark® and VeraTag® assay, respectively. Predictors of persistence on protocol (PP) were studied by Cox univariate and multivariate analysis. Nineteen patients were enrolled. Median overall survival was 43 months and median PP was 3.8 months (0.8-38.8+), with 4 patients (21.1%) persisting on single agent
trastuzumab or
lapatinib for longer than 12 mo (14.9-38.8 + mo). Seventeen patients were evaluable for PP. Gene expression analysis revealed that high expression of the 17q12-21 amplicon genes HER2 and GRB7, and the PAM50 HER2-enriched intrinsic profile, were significantly associated with longer PP. Conversely, high expression of
luminal-related genes such as PGR, MDM2 or PIK3CA, or the PAM50
luminal intrinsic profile correlated with reduced PP. Moreover, increasing H2T/p95 ratio was found to be significantly associated with longer PP (HR 0.56 per 2-fold increase in H2T/p95, P = 0.0015). Our data suggest that patients belonging to the "HER2-enriched" subtype and/or having high H2T/p95
protein expression ratio are exquisitely sensitive to anti-HER2 agents. MBC patients with these
tumors could be candidates for studies aimed at establishing
chemotherapy-free regimens.