Potential Biomarkers of Long-term Benefit from Single-agent Trastuzumab or Lapatinib in HER2-positive Metastatic Breast Cancer

Gene expression data of HER2+ breast tumor samples Increasing evidence indicates that a subset of patients with HER2-positive breast cancer may achieve significant clinical benefit with anti-HER2 targeted therapy without chemotherapy. Thus, identification of biomarkers of long-term benefit from anti-HER2 agents is needed, especially in the metastatic setting. In the HERLAP study (NCT00842998), patients with HER2-positive metastatic breast cancer were randomized to trastuzumab or lapatinib as first-line therapy. Patients showing radiological signs of tumor regression after 8 weeks of treatment were allowed to continue on single agent anti-HER2 therapy until disease progression. Chemotherapy was added to anti-HER-2 therapy in patients failing to achieve tumor regression at the 8-week evaluation and those progressing at any time. Expression analysis of 105 selected genes was performed from formalin-fixed paraffin-embedded in 17 primary tumor samples. The research-based PAM50 intrinsic subtypes were also identified. The association of the expression of each biomarker with clinical outcome endpoints was evaluated. Nineteen patients were enrolled. In 4 patients (21.1%) we observed disease control lasting longer than 12 months with single agent anti-HER2 therapy (range 14.9-38.8 months). High expression of 17q12-21 amplicon genes HER2 and GRB7, and the PAM50 HER2-enriched intrinsic profile, were found significantly associated with 8-week overall response rate and with the duration of disease control during single agent anti-HER2 therapy. Conversely, high expression of luminal-related genes such as PGR, MDM2 or PIK3CA, or the PAM50 luminal intrinsic profile, was found associated with reduced benefit from single agent anti-HER2 therapy. Conclusions: Our data indicate that gene expression-based biomarkers can identify patients with HER2-positive metastatic breast cancer that benefit substantially from single agent chemo-free anti-HER2 targeted therapy. In the study presented here, a well-defined cohort of 21 breast cancer cases from the HERLAP trial, was used to acquire expression profiles of a total of 105 unique genes