Background: By 2018, Immune Checkpoint Inhibitor (ICI) drugs had gained FDA approval for the treatment of several cancers including melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinoma (RCC). Recommendations for treatment duration for ICI therapy varies and is often used until either progression of disease or intolerance from toxic effects. Blumenthal et al showed that there is a positive correlation between real-world time to discontinuation (rwTTD) and progression free survival. We report the rwTTD of ICI drug use in first-line of therapy (LOT1) among enrollees diagnosed with melanoma, NSCLC, and RCC between 2015 and 2018, as well as ICI utilization in second-line therapy. Methods: A cohort of patients treated for these 3 cancers between 2015 and 2018 was identified using de-identified data from the Optum Labs Data Warehouse and clinical information from the Optum Cancer Guidance Program’s electronic prior authorization (ePA) platform. De-identified administrative claims data were then linked to ePA information at the patient level to identify details of treatment received and duration of treatment. Eligible patients were enrolled in a commercial or Medicare Advantage (MA) plan and required to initiate treatment within 6 months of diagnosis, enrolled at least 6 months prior to diagnosis date (in order to ensure this was the LOT1) and at least thirty days after start of first identified treatment regimen (in order to identify the full treatment regimen). ICI regimens are defined as those with an ICI drug received within the first 30 days of the LOT1 start date. Duration of ICI use was defined as number of days from LOT1 start to date of last ICI administration in LOT1. We estimate rwTTD accounting for censoring via SAS PROC LIFETEST. Results: In this population, we identified 844 eligible patients with these 3 cancers who received LOT1 ICI therapy from 2015 - 2018. NSCLC is the most common cancer treated with an ICI (N = 598). Median rwTTD varied between 172 and 191 days across these 3 cancers. 68% of melanoma patients remained on LOT1 ICI treatment at 90 days decreasing to 30% at 1 year, while 74% of NSCLC remained on LOT1 ICI for at least 90 days and 40% of RCC patients for 1 year. We observed that of individuals who had an ICI in LOT1, 18% of those with NSCLC moved on to an ICI in LOT2, 39% of those with Melanoma, and 25% of those with RCC. Conclusions: Median rwTTD and the percent of patients remaining on ICI treatment at 90 and 180 days in LOT1 was similar among the three cancers. However, RCC patient are more likely to remain on LOT1 ICI (40%) than those being treated for Melanoma and NSCLC.