Impact of radiotherapy schedule on survival of patients treated with immune-checkpoint inhibitors for advanced melanoma and non-small cell lung cancer

Purpose: Preclinical and clinical data suggest a potential benefit in the addition of radiotherapy (RT) to immune-checkpoint inhibitors (ICI) during the treatment of advanced cancers. Nevertheless, the ideal patients for this approach and the optimal RT regimen is still debated.

Material and methods: The aim of this study was to determine the effect RT schedule has on survival for advanced non-small cell lung cancer and melanoma patients (pts) treated with ICI (anti-PD1 or anti-CTLA4) and concomitant RT.

Results: A total of 58 pts were identified, of which 26 received RT concomitantly with ICI while the remaining 32 pts were treated with RT at the time of progression under ICI. The RT parameters associated with outcome include dose per fraction, biological effective dose, RT to all targets and lung irradiation. Independent predictors of improved progression-free survival were lung irradiation, melanoma histology, oligometastatic status (<6 metastasis), presence of liver metastasis, PNN<7000/mm³ and normal LDH. Independent predictors of improved overall survival were melanoma histology and normal LDH. Among pts who were irradiated at progression, 68.7% had an overall clinical benefit and had a median extension of ICI use by 2.3 months (range: 0-29.1), among which 2 presented with an abscopal effect.

Conclusions: The irradiation of lung metastases may increase survival in patients under ICI. RT at progression could prolong the use of ICI, and neutrophilia and LDH should be considered during patient selection of this combined RT/ICI approach.