CLO20-042: The HER2 FISH Ratio is a Predictor of Pathologic Complete Response Among Patients With HER2+ Breast Cancer Receiving Neoadjuvant Anti-HER2 Doublet Therapy Without Chemotherapy

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  • a Vanderbilt University Medical Center, Nashville, TN
  • b Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, MD
  • c Vanderbilt-Ingram Cancer Center, Nashville, TN

The optimal strategy for neoadjuvant treatment of human epidermal receptor (HER2) positive breast cancer is evolving. Pathologic complete response (pCR) in HER2-positive breast cancer is a primary endpoint for neoadjuvant trials because it is associated with improved event-free survival and overall survival. Phase II and III clinical trials of neoadjuvant dual anti-HER2 therapy with or without chemotherapy have shown similarly high rates of pCR between treatment groups. Biomarkers that predict pCR may identify who will most benefit from dual HER2 blockade without chemotherapy in the neoadjuvant setting. Fluorescence in situ hybridization (FISH) from tissue biopsy derives the HER2/CEP17 ratio, where amplification (ratio >2) positively predicts response to anti-HER2 therapy. It remains unclear whether higher HER2 FISH ratios may be predictive of pCR among patients treated with neoadjuvant dual HER2 blockade without chemotherapy. We examined whether pCR to neoadjuvant anti-HER2 doublet therapy without chemotherapy is associated with the level of HER2 amplification, hypothesizing that patients with higher HER2 FISH ratios would be more likely to achieve pCR. Patients were participating in clinical trials at Vanderbilt-Ingram Cancer Center between May 2009 and April 2017, and were included if they had histologically-confirmed stage I-III invasive HER2-positive breast cancer, received neoadjuvant HER2 doublet treatment without chemotherapy, and underwent definitive breast surgery. The three trials’ treatment arms were trastuzumab plus lapatinib for 12-24 weeks, trastuzumab emtansine plus pertuzumab for 6 cycles, and pertuzumab plus trastuzumab for 6 cycles. Covariates included age, hormone receptor status, tumor grade, and treatment arm. pCR was defined as ypT0 ypN0 or ypT0/is ypN0 at the time of definitive breast surgery following treatment. All 56 eligible patients were included in the analysis of which 52 percent achieved pCR. The median HER2 FISH ratio was 9.4 (SD ± 5.5). Increasing HER2 FISH ratios up to 11 were associated with higher rates of pCR to neoadjuvant HER2 doublet therapies (p = 0.001). Above HER2 FISH ratios of 11, no additional increase in the likelihood of pCR was observed though it remained positively associated with pCR (p = 0.0150). Our findings encourage future investigation of identifying a clinical subtype in breast cancer with high HER2 FISH amplification that may be exquisitely sensitive to dual HER2 therapy without chemotherapy.

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Corresponding Author: Eric Lander, MD
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