ABSTRACT: Improvement in overall survival by immune checkpoint inhibitors (ICI) treatment in clinical trials encourages their use for late-stage melanoma. However, in the real-world, heterogeneity of population, such as older patients with multimorbidity, may lead to a slower diffusion of ICIs. The objective of this study was to examine the association of multimorbidity and other factors to ICI use among older patients with late-stage melanoma using real world data.A retrospective cohort study design with a 12-month baseline and follow-up period was adopted with data from the linked Surveillance, Epidemiology, and End Results cancer registry/Medicare database. Older patients (>65 years) with late-stage (stage III/IV) melanoma diagnosed between 2012 and 2015 were categorized as with or without multimorbidity (presence of 2 or more chronic conditions) and ICI use was identified in the post-index period. Chi-square tests and logistic regression were used to evaluate factors associated with ICI use.In the study cohort, 85% had multimorbidity, 18% received any treatment (chemotherapy, radiation, and/or ICI), and 6% received ICI. Only 5.5% of older patients with multimorbidity and 6% without multimorbidity received ICIs. Younger age, presence of social support, lower economic status, residence in northeastern regions, and recent year of diagnosis were significantly associated with ICI use; however, multimorbidity, sex, and race were not associated with ICI use.In the real-world clinical practice, only 1 in 18 older adults with late stage melanoma received ICI, suggesting slow pace of diffusion of innovation. However, multimorbidity was not a barrier to ICI use.