Long-term Local Control and Overall Survival After Radiotherapy in Oligoprogressive Patients During Treatment With Checkpoint Inhibitors

Background/Aim: Recent studies described the safety and clinical utility of combined anti-programmed cell death protein-1 (anti-PD1) checkpoint inhibition with radiotherapy. However, long-term follow-up data are lacking. Abscopal effects have been hypothesized, though clinical proof is still scarce. Patients and Methods: We analyzed the efficacy and toxicity of combined (stereotactic) radiotherapy and antiPD1 in consecutive oligoprogressive melanoma and non-small cell lung cancer (NSCLC) patients who were irradiated for 1 to 3 progressive metastases during anti-PD-1 in our institute between January 2017 and January 2019 and verified one-dimensional RECIST measurements by volumetric assessments. Results: Out of 361 patients, 11 melanoma and 5 NSCLC patients were included in this series. Radiotherapy was applied after a median of 11 months (range=1-30 months) from the start of anti-PD1 treatment. No increased risk of adverse events for the combined treatments was observed. With a median follow-up of 4.9 years since the start of anti-PD1, 69% of patients were alive. Six of 16 patients had stable disease after a median follow-up of 4.1 years after radiotherapy. Abscopal effects were suspected in three out of 16 patients. However, if volumetric assessment was used, two of these patients already had tumor shrinkage prior to radiotherapy, not detected by one-dimensional measurements. Conclusion: Stereotactic radiotherapy for oligoprogressive disease during PD1-inhibition can induce long-term disease control. Although abscopal effects were suspected in three patients, they were not confirmed with volumetric assessment in two patients. The discrepancy found between one-dimensional and volumetric response assessment argues for including volumetric assessment in further studies.