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SABCS 2023: Adding Atezolizumab to Neoadjuvant Therapy for High-Risk, HER2-Positive Breast Cancer

By: Julia Fiederlein Cipriano, MS
Posted: Monday, December 18, 2023

The addition of atezolizumab to neoadjuvant trastuzumab, pertuzumab, carboplatin, and paclitaxel (HPCT) did not significantly increase the pathologic complete response rate in patients with HER2-positive, high-risk early or locally advanced breast cancer, based on the results of the multicenter phase III APTneo Michelangelo trial, presented during the 2023 San Antonio Breast Cancer Symposium (SABCS; Abstract LBO1-02). However, according to Luca Gianni, MD, of Fondazione Michelangelo, Milan, Italy, and colleagues, adding atezolizumab to anthracycline and cyclophosphamide followed by HPCT led to an improvement vs HPCT plus atezolizumab.

Patients were randomly assigned to receive neoadjuvant HPCT alone (arm A; n = 223) or in combination with atezolizumab (arm B; n = 438). Arm B was further randomly assigned to receive either anthracycline and cyclophosphamide plus atezolizumab followed by HPCT plus atezolizumab (arm B1; n = 218) or HPCT plus atezolizumab (arm B2; n = 220).

The pathologic complete response rate was not found to be significantly higher with atezolizumab vs without (57.8% vs 52.0%; adjusted hazard ratio [HR] = 1.33; P = .091); a nonsignificant difference was also observed between arms B1 and B2 (61.9% vs 53.6%; adjusted HR = 1.402; P = .089). Arm B1 vs A was found to have a 9.9% significantly higher pathologic complete response rate. In all arms, patients with high levels of stromal tumor–infiltrating lymphocytes (≥ 30%) and PD-L1–positive tumors seemed to have a greater likelihood of achieving a pathologic complete response.

Serious adverse events were documented in 14.1% and 6.8% of patients treated with and without atezolizumab, respectively, after the start of therapy (P = .0064). A total of 16.7% of patients in arm B1 and 11.6% of those in arm B2 experienced such toxicities. According to the investigators, immune-related serious adverse events occurred infrequently and were similar between arms B1 (4.7%) and B2 (7.8%). No adverse events of grade 5 were reported.

Disclosure: For full disclosures of the study authors, visit

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