Safety of Combining Radiation Therapy and Antibody Drug Conjugates in Advanced Urothelial and Other Cancers.

Antibody drug conjugates (ADCs) such as enfortumab vedotin and sacituzumab govitecan are novel treatments increasingly used for metastatic urothelial carcinoma. There is limited data evaluating their safety when combined with radiation therapy (RT). A bi-institutional retrospective analysis was performed to characterize toxicity in patients who received RT within 6 months of receipt of ADC. Patients were stratified by intensity of RT (higher vs lower), site of RT, and RT timing relative to ADC. One hundred three patients received 166 courses of RT (66% lower vs 34% higher intensity). In 11% of courses, RT was directed to the pelvis including the bladder. Of 77 (46%) RT courses concurrent with ADC, 7 (12%) patients experienced grade 1-2 toxicity, and 10 (13%) patients experienced grade 3-5 toxicity. All of these were attributed to known ADC toxicities, and only one was possibly influenced by the addition of RT. No patients receiving RT to the bladder experienced high-grade toxicity. This retrospective study thus found no added safety events for patients receiving RT with ADCs, even when administered concurrently. Further data to validate these findings is needed as the use of both ADCs and RT increases in patients with urothelial carcinoma.