Purpose: We retrospectively evaluated the tumor regression after radiotherapy in combination with the immune checkpoint inhibitor nivolumab for metastatic melanoma.
Materials and methods: We evaluated the extracranial metastatic melanoma lesions to which concomitant radiotherapy with nivolumab was administered from June 2015 to February 2017. Tumor volume and maximum diameter were measured at the time of pre-radiotherapy and best response, and the tumor reduction rate was assessed in two ways that our hospital adopts: tumor volume and diameter.
Results: Seven lesions in five patients were evaluated. The median time from the start of nivolumab treatment to the start of radiotherapy was 5 months (range 0-22 months). The objective response rate was 85.7% in the evaluation by tumor volume and 42.9% by maximum diameter of the tumor. The objective complete response rate was 28.6% in evaluation by tumor volume and 14.3% by maximum dia. The 1-year tumor control rate was 62.5%. The 1- and 2-year overall survival rate after nivolumab treatment were 75% and 50%, respectively. Two patients who obtained a complete response had presented with vitiligo.
Conclusion: The combination of radiotherapy and nivolumab treatment produced favorable responses. Vitiligo may be correlated with a good response to concomitant radiotherapy with nivolumab.
Keywords: Abscopal effects; Extracranial metastases; Malignant melanoma; Nivolumab; Radiotherapy.