Improved infield response rates and overall survival in patients with metastatic melanoma receiving higher biological equivalent doses of radiation with ipilimumab

There is a growing body of evidence that combining radiotherapy with ipilimumab might improve the survival and response rates in patients with metastatic melanoma. However, the patient and treatment variables that predict for improved outcomes have not been well defined. We conducted a retrospective analysis of 69 patients treated with ipilimumab and radiotherapy for metastatic melanoma at a single institution from May 2011 to June 2015. Demographic, clinical, and treatment factors were recorded, and end points of interest included infield and global complete response (CR) after the completion of radiation and ipilimumab based on the RECIST criteria (v1.1), and overall survival (OS). A bivariate and multivariate analysis was then performed to assess the relationship between outcomes and patient variables. In the multivariate analysis, infield CR was significantly associated with completing a full course of ipilimumab, a higher BED, and a smaller size of metastatic area treated. Global CR was significantly associated with increased age and giving radiotherapy to all areas of disease. OS was significantly associated with completing a full course of ipilimumab and a higher BED. Interestingly, after a multivariate analysis, higher BED was associated with an improved infield CR (p = 0.0281) and was not associated with an improved global CR (p = 0.5284) but was marginally associated with improved OS (p = 0.0545). Our findings suggest that the rate of a global CR is independent of the dose of radiation given, but the rate of infield CR and OS might improve with higher doses.