Effect of neoadjuvant pertuzumab-containing regimens on pathologic complete response rates in stage II-III HER2-neu positive breast cancer: A retrospective, single institutional experience.

Abstract

580 Background: Pertuzumab (P) in combination with trastuzumab (H) based chemotherapy is currently FDA- approved as a standard neoadjuvant treatment for patients with clinical stage II-III HER2-positive (HER2+) breast cancer (BC). The chemotherapy backbone of HER2-targeted therapy varies and may include taxane (T) and/or anthracycline (A), or carboplatin (C). The goal of this study was to retrospectively evaluate the pathologic complete response (pCR) rate for HP-containing regimens compared to H containing regimens for stage II-III HER2+ BC. Methods: We identified all patients (n = 1150) with stage II-III HER2+ BC who received neoadjuvant HER2-targeted therapy from 2005 to 2016 through an institutional database. All patients underwent primary breast and lymph node surgery. pCR was defined as ypT0/is, ypN0. Univariate/multivariate logistic regression and chi-squared test for comparing proportions was used for the statistical analysis. Results: pCR was significantly higher for the HP group (n = 200) compared to the H group (n = 950): 44% vs. 41%, odds ratio = 1.8 (95% CI = 1.3, 2.5; P = 0.0002). Even with adjustment for all clinically significant factors (age, stage, tumor grade, hormone receptor (HR) status, A or C exposure), the improvement was statistically significant (adjusted OR = 2.1 (95% CI = 1.5, 2.9; P < 0.0001). The pCR rate by stage and HR status for the HP group is 62% vs. 55% (stage II vs. III) and 71% vs. 51% (HR- vs. HR+). The effect of P was not modified by HR status (HR-, OR = 2.3; HR+, OR = 1.7, P = 0.39) or by A (A-yes, OR = 1.8; A-no, OR = 2.6) (P = 0.28 for interaction) or C (C-yes, OR 2.6; C-no, OR = 1.8) (P = 0.30 for interaction). P was significantly more likely to be given to patients without A (36% vs. 10%, P < 0.0001) and more likely to be given to patients with C (30% vs. 14%, P < 0.001). In both groups, significant predictors of pCR were found to be stage, HR status, and C exposure. Conclusions: Pertuzumab containing regimens yield higher pCR rates compared to non-Pertuzumab containing regimens in stage II- III HER-2 positive breast cancer. The effect of Pertuzumab is not modified by anthracycline or carboplatin use.