Systemic Therapy for Patients with HER2-Positive Breast Cancer and Brain Metastases: A Systematic Review and Meta-Analysis

Radiation therapy, tissue radiosensitization, and potential synergism in the era of novel antibody-drug conjugates

Antibody-drug conjugates (ADCs) represent a therapeutic class of agents designed to selectively deliver cytotoxic payloads to cancer cells. With the increasingly positioning of ADCs in the clinical practice, combinations with other treatment modalities, including radiation therapy (RT), will open new opportunities but also challenges. This review evaluates ADC-RT interactions, examining therapeutic synergies and potential caveats. ADC payloads can be radiosensitizing, enhancing cytotoxicity when used in combination with RT. Antigens targeted by ADCs can have various tissue expressions, resulting in possible off-target toxicities by tissue radiosensitization. Notably, the HER-2-directed ADC trastuzumab emtansine has appeared to increase the risk of radionecrosis when used concomitantly with brain RT, as glial cells can express HER2, too. Other possible organ-specific effects are discussed, such as pulmonary and cardiac toxicities. The lack of robust clinical data on the ADC-RT combination raises concerns regarding specific side effects and the ultimate trade-off of toxicity and safety of some combined approaches. Clinical studies are needed to assess ADC-RT combination safety and efficacy.

Trastuzumab Deruxtecan: A Review in Unresectable or Metastatic HER2-Positive Breast Cancer

Trastuzumab deruxtecan (Enhertu^®) is a human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate approved in several countries, including the USA and those of the EU, for adults with unresectable or metastatic HER2-positive breast cancer who have previously received at least one prior anti-HER2-based regimen. In a pivotal phase 3 trial in this setting, intravenous trastuzumab deruxtecan demonstrated prolonged progression-free survival compared with trastuzumab emtansine (previously the recommended second-line therapy in this indication). Trastuzumab deruxtecan had a generally manageable safety and tolerability profile. Common treatment-related adverse events included haematological and gastrointestinal disorders. Interstitial lung disease (ILD)/pneumonitis is associated with a regulatory warning and requires careful monitoring. In conclusion, trastuzumab deruxtecan is a valuable new treatment option for HER2-positive breast cancer, having been shown to be effective with a generally manageable safety and tolerability profile in adults with unresectable or metastatic disease who have received one or more prior anti-HER2-based regimens.