Efficacy of Endocrine Therapy Plus Trastuzumab and Pertuzumab vs De-escalated Chemotherapy in Patients with Hormone Receptor–Positive/ERBB2-Positive Early Breast Cancer

Importance Combination of chemotherapy with (dual) ERBB2 blockade is considered standard in hormone receptor (HR)-positive/ ERBB2 -positive early breast cancer (EBC). Despite some promising data on endocrine therapy (ET) combination with dual ERBB2 blockade in HR-positive/ ERBB2 -positive BC, to our knowledge, no prospective comparison of neoadjuvant chemotherapy vs ET plus ERBB2 blockade in particular with focus on molecular markers has yet been performed. Objective To determine whether neoadjuvant de-escalated chemotherapy is superior to endocrine therapy, both in combination with pertuzumab and trastuzumab, in a highly heterogeneous HR-positive/ ERBB2 -positive EBC. Design, Setting, and Participants This prospective, multicenter, neoadjuvant randomized clinical trial allocated 207 patients with centrally confirmed estrogen receptor–positive and/or progesterone receptor–positive (>1%) HR-positive/ ERBB2 -positive EBC to 12 weeks of standard ET (n = 100) vs paclitaxel (n = 107) plus trastuzumab and pertuzumab. A total of 186 patients were required to detect a statistically significant difference in pathological complete response (pCR) (assumptions: 19% absolute difference in pCR; power, ≥80%; 1-sided Fisher exact test, 2.5% significance level). Interventions Standard ET (aromatase inhibitor or tamoxifen) or paclitaxel, 80 mg/m 2 , weekly plus trastuzumab and pertuzumab every 21 days. Main Outcomes and Measures The primary end point was pCR (ypT0/is, ypN0). Secondary end points included safety, translational research, and health-related quality of life. Omission of further chemotherapy was allowed in patients with pCR. PAM50 analysis was performed on baseline tumor biopsies. Results Of the 207 patients included (median [range] age, 53 [25-83] years), 121 (58%) had cT2 to cT4 tumors, and 58 (28%) had clinically node-positive EBC. The pCR rate in the ET plus trastuzumab and pertuzumab arm was 23.7% (95% CI, 15.7%-33.4%) vs 56.4% (95% CI, 46.2%-66.3%) in the paclitaxel plus trastuzumab and pertuzumab arm (odds ratio, 0.24; 95% CI, 0.12-0.46; P < .001). Both immunohistochemical ERBB2 score of 3 or higher and ERBB2 -enriched subtype were independent predictors for pCR in both arms. Paclitaxel was superior to ET only in the first through third quartiles but not in the highest ERBB2 quartile by messenger RNA. In contrast with the paclitaxel plus trastuzumab and pertuzumab arm, no decrease in health-related quality of life after 12 weeks was observed in the ET plus trastuzumab and pertuzumab arm. Conclusions and Relevance The WSG-TP-II randomized clinical trial is, to our knowledge, the first prospective trial comparing 2 neoadjuvant de-escalation treatments in HR-positive/ ERBB2 -positive EBC and demonstrated an excellent pCR rate after 12 weeks of paclitaxel plus trastuzumab and pertuzumab that was clearly superior to the pCR rate after ET plus trastuzumab and pertuzumab. Trial Registration ClinicalTrials.gov Identifier: NCT03272477