Multinational prospective cohort study of adverse events after metastases-directed stereotactic radiotherapy and biological cancer therapy

Metastases-directed stereotactic radiotherapy (SRT) is increasingly performed in patients with metastatic or oligometastatic cancer treated with biological cancer therapy (BCT), including immunotherapy and targeted therapies. Little is known about potential interactions between SRT and BCT. The multinational prospective TOaSTT study (‘Toxicity and Efficacy of Comined Stereotactic Radiotherapy and Systemic Targeted or Immune Therapy’) investigated adverse events after metastases-directed SRT with concurrent BTC in patients with metastatic or oligometastatic cancer. In total, 514 SRTs (271 cranial and 243 extracranial) concurrent with BCT were performed in 433 patients. The study found a low risk (<10%) of severe acute or late adverse events. Uninterrupted treatment with BCT during SRT was not associated with significantly increased severe adverse events. The authors conclude that these results suggest that the favorable safety profile of metastases-directed SRT persists in combined modality treatments.