Comparative safety of concurrent adjuvant trastuzumab emtansine versus trastuzumab with radiotherapy in HER2-positive early breast cancer.

Authors

Mine Aysan, Bahadir Koylu, Ayberk Bayramgil, Dilek Unal, Banu Karaalioğlu, Ahmet Bilici, Fatih Selçukbiricik, Ozcan Yildiz, Ömer Fatih Olmez

Published in

The oncologist. Sep 21, 2026. Epub Sep 21, 2026.

Abstract

Real-world comparative data on the safety of adjuvant trastuzumab emtansine (T-DM1) versus trastuzumab with concurrent radiotherapy (RT) in HER2-positive early breast cancer (BC) remain limited.
In this retrospective, multicenter study, we included 133 patients with HER2-positive early-stage BC treated with neoadjuvant therapy, surgery, and adjuvant systemic therapy administered concurrently with RT at four hospitals. Patients received adjuvant T-DM1 (n = 50) if residual disease was present, or trastuzumab (n = 83) if a pathologic complete response was achieved. Toxicities were graded according to CTCAE criteria. A post-hoc power analysis indicated 80% power to detect an absolute between-group difference in toxicity rates of ≥ 25%.
The T-DM1 group had poorer performance status, higher nodal stage, and more intensive neoadjuvant regimens. RT parameters were balanced between groups (median dose 50 Gy, 25 fractions; p > 0.05 for all comparisons). T-DM1 was associated with higher rates of thrombocytopenia (70% versus 36.1%, p < 0.001), ALT elevation (20% versus 4.8%, p = 0.008), AST elevation (24.5% versus 2.4%, p < 0.001), and early pulmonary toxicity (48.8% versus 24.1%, p = 0.017), with events predominantly grade 1. In sensitivity analyses adjusting for pertuzumab exposure, T-DM1 associations remained significant for thrombocytopenia (adjusted odds ratio [OR] = 3.85, p = 0.001), ALT elevation (adjusted OR = 4.12, p = 0.026), and early pulmonary toxicity (adjusted OR = 2.64, p = 0.034).
Concurrent adjuvant T-DM1 and RT demonstrated higher but manageable hematologic, hepatic, and pulmonary toxicity compared with trastuzumab. These hypothesis-generating findings require validation in prospective studies.

PMID:
42768455
Bibliographic data and abstract were imported from PubMed on 22 Sep 2026.

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