Abstract P3-10-25: Clinicopathologic factors associated with pCR to neoadjuvant anti-HER2-directed chemotherapy

Abstract

Abstract Background: While the use of neoadjuvant therapy has become the standard of care in certain locally advanced breast cancers, questions remain regarding the optimal chemotherapeutic regimen as well as biologic and patient-specific predictors of pathologic complete response. In this study, we examined patient and tumor-specific characteristics associated with increased prediction of pathologic complete response (pCR) to neoadjuvant anti-HER2-directed chemotherapy. Methods: 204 patients who received neoadjuvant anti-HER2-directed chemotherapy at our institution from 2006-2016 were included in this retrospective study. Univariate analyses were performed to analyze the relationships of multiple clinical and pathologic features to pCR rate. Multivariate analysis was also performed to evaluate the relative impact of specific pathologic characteristics on pCR rate. Results: Among 204 patients with HER2 overexpressing breast cancers treated with neoadjuvant chemotherapy, 52.7% achieved pCR. Pathologic complete response was positively associated with high tumor grade (61.0% grade 3 in pCR group vs 39.0% in non-pCR group, P=0.23) and high Ki67 index (mean Ki67 59.1 in pCR group vs 47.4 in non-pCR; P= 0.015). It was also associated with HER2 IHC 3+ (57.1% in pCR group vs 42.9% in non-pCR, p=0.029), HER2 copy number (mean copy number 16.8 in pCR group vs 12.4 in non-PCR, p-0.004), and HER2/CEP 17 ratio (mean ratio 6.42 in pCR group vs 5.17 in non-pCR; P= 0.046). Rates of HER2 FISH positivity were equal in the pCR and non-pCR groups (50.8% vs 49.2%, p=0.062). Multivariate analysis demonstrated that higher Ki67 index and higher HER2/CEP17 ratio are significant predictors of pCR after adjusting for other covariates (odds ratio for Ki67 1.03 (1.06-1.49), p=0.002; for HER2/CEP17 ratio OR 1.26 (1.06-1.49), p=0.009). Conclusions: In HER2 positive breast cancers, a higher Ki67 index as well as higher HER2/CEP17 ratios are associated with an increased pCR rate and may be useful as predictors of response prior to neoadjuvant therapy. Our results also demonstrate HER2 IHC to be a stronger predictor than HER2 FISH of response to upfront therapy. Larger studies would be useful as this association, if confirmed, may have relevance to clinical practice. Citation Format: Meisel JL, Suo A, Taylor CE, Zhang C, Li X. Clinicopathologic factors associated with pCR to neoadjuvant anti-HER2-directed chemotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-10-25.