Safety of combining radiation therapy and antibody-drug conjugates in patients with breast cancer: a systematic review and meta-analysis

Background and purpose The treatment landscape for breast cancer has undergone significant advancements in the recent years, with the introduction of several new anticancer agents, especially those belonging to the antibody-drug conjugates (ADCs) class. However, there exists a lack of comprehensive evidence regarding the safety profile of combining ADCs with radiation therapy (RT). Here we provide a summary of the available data on the safety of combining RT with ADCs in both early and metastatic breast cancer settings as part of updating European Society for Radiotherapy and Oncology (ESTRO) consensus.Materials and methods This systematic review and meta-analysis project is part of the Second International Consensus Recommendations by the ESTRO Guidelines Committee on integrating RT with targeted treatments for breast cancer. A thorough literature search was conducted using the PUBMED/MedLine, Embase, and Cochrane databases to identify original studies focusing on the safety profile of combining ADCs with RT.Results After applying eligibility criteria, a total of 29 studies published between 2014 and 2026 were included, representing 3,817 patients who received at least one RT course concurrently to an ADC. The pooled grade ≥ 3 radiation necrosis rate across all studies reporting this endpoint was 5% (95% CI: 1-12%; I2 = 85.9%). In the intracranial RT setting, the pooled grade ≥ 3 treatment-related adverse event rate was 8% (95% CI: 3-15%; I2 = 81.7%), with T-DM1 studies showing the highest sub-total estimate of 13% (95% CI: 1-34%). Grade ≥ 3 pneumonitis was rare across all settings (pooled 0%; 95% CI: 0-1%; 12 studies), as well as grade ≥ 3 skin side effects (pooled 0%; 95% CI: 0-1%; 13 studies) were rare across all settings.Conclusion RT can be safely delivered alongside ADCs therapy in most clinical settings, with severe complications occurring infrequently. The available evidence supports the use of conventional extracranial RT during treatment with T-DM1, T-DXd, and SG, provided that routine safety monitoring is maintained. In contrast, intracranial stereotactic RT remains the setting in which caution is warranted, particularly in patients receiving T-DM1, for whom an increased risk of radiation necrosis has been consistently reported. Current data does not suggest a similar risk signal for T-DXd or SG. Radiation necrosis; Stereotactic radiotherapy.