‘Le Roi est mort, vive le Roi’: new roles of radiotherapy in the treatment of lymphomas in combination with immunotherapy.

ABSTRACT Background immunotherapy (IT), including checkpoint inhibitors (CIs) and Chimeric Antigen Receptor T cell therapy (CAR-T) revolutionized the treatment of relapsing or refractory (r/r) lymphoma. Several preliminary experiences evaluated concomitant administration of radiotherapy and IT. Methods we performed a systematic review of current literature as of March 30, 2020. A total of 1090 records was retrieved, 42 articles were selected on the basis of title and abstract and, after the removal of analyses with no original data or insufficient clinical information, 28 papers were included in the review. Results previous studies were mostly represented by case reports/series or small cohorts. Nonetheless, combination of radiotherapy and CIs or CAR-T led to promising outcomes, resulting in extremely high rates of complete response and improving progression free and overall survival compared with data from recent clinical trials. Combination of RT and CIs had a fair toxicity profile with no reports of severe side effects. Within the limits of the small cohorts retrieved, RT seems a superior option compared with systemic treatment as a ‘bridge’ to CAR-T and could as well reduce severe complications rates. Radiotherapy could elicit immune response against lymphoma, as demonstrated by multiple cases of abscopal effect and its inclusion in anti-neoplastic vaccines protocols. Conclusion The results of this review warrant the evaluation of combination of RT and immunotherapy in larger and preferably prospective and randomized cohorts to confirm these preliminary impressive outcomes. The optimal dose, fractionation and timing of RT still have to be clarified.