Use of extracranial radiation therapy in metastatic melanoma patients receiving immunotherapy

Purpose: Explore the patterns of use of extracranial radiation therapy (RT) in metastatic melanoma patients receiving immunotherapy, its potential association with OS, the impact of the site and timing of RT on clinical outcomes when combined with immunotherapy. Materials and methods: Patients with extracranial metastatic melanoma who received immunotherapy with or without extracranial RT from 2004 to 2013 were obtained from the National Cancer Database. Multivariable Cox regression analysis was used to evaluate factors associated with overall survival (OS). Subset analyses comparing outcomes in patients receiving RT to bone metastases versus soft tissue metastases were also performed. OS was compared using the Kaplan–Meier and log-rank statistics. Results: A total of 1675 patients were identified: 1387 received immunotherapy alone and 288 received immunotherapy plus RT. An increase in the utilization of RT as well as SBRT was noted over time. The rate of RT use was 11.5% (0% with SBRT) in 2004 and gradually rose to 19.8% (27.0% with SBRT) in 2013 (P = 0.04). The median OS was 15.4 vs. 19.4 months in the immunotherapy plus RT and immunotherapy alone groups, respectively (P = 0.02). However, on multivariable analysis, RT was not associated with worse OS. The poor OS in the RT group was confined to the patients who received RT to bone metastases, but not in patients who received RT to soft tissue metastases. In subset analyses of patients irradiated to soft tissue, RT administered at least 30 days before immunotherapy was associated with a higher OS than RT administered within 30 days or 30 days after immunotherapy: median 26.1 months vs. 16.0 months (P = 0.009) vs. 15.4 months (P = 0.004), respectively. Conclusions: This study demonstrates that extracranial RT plays an increasing role in the management of metastatic melanoma patients in the era of immunotherapy. The site and the timing of RT may have important interaction with immunotherapy, and need to be carefully considered in future clinical trials.