AbstractObjective:To estimate the costs of adverse events (AEs) in patients aged 65 years with metastatic renal cell carcinoma (mRCC).Methods:Retrospective study using the linked Surveillance, Epidemiology and End Results (SEER) Medicare database. Study subjects consisted of persons in SEER-Medicare, aged 65 years, with evidence of newly diagnosed mRCC between January 1, 2007 and December 31, 2007. Adverse events of interest consisted of Grade 3 or 4 toxicities that have been reported with frequency 5 in randomized controlled trials of sunitinib, sorafenib, bevacizumab, and pazopanib (i.e., targeted therapies for mRCC), and included abdominal pain, back pain, diarrhea, dyspnea, extremity pain, fatigue/asthenia, hand-foot syndrome, hypertension, lymphopenia, nausea/vomiting, neutropenia, proteinuria, and thrombocytopenia. Patients in SEER-Medicare with these events were identified based on ICD-9-CM diagnosis codes on Medicare claims. For each AE of interest, costs were tallied among evented patients over 30 days, beginning with the date of each patient’s first mention of the AE, and were compared with those of non-evented patients over a similar 30-day period beginning with an identical ‘shadow’ index date. Total costs were compared on an unadjusted basis and with adjustment for differences in baseline characteristics using a generalized linear model.Results:A total of 881 patients with mRCC met study entry criteria; 60 of these patients had Medicare claims with mention of one or more AEs of interest. Events occurring with frequency >20 included abdominal pain, dyspnea, and fatigue/asthenia; 10–20 of study subjects had encounters for back pain, extremity pain, and nausea/vomiting. Mean (standard deviation) total cost of care over 30 days was substantially higher among patients with AEs (13,944 [14,529]) compared with those without mention of these events (1878 [5264]). Adjusting for differences in baseline characteristics, the mean (95 confidence interval) difference in costs between evented and non-evented patients was 12,410 (9217–16,522). Study limitations include problems in event ascertainment due to inaccuracies in ICD-9-CM coding on Medicare claims data, and restriction of the study population to patients with metastatic involvement at initial diagnosis of RCC.Conclusions:Costs of care are substantially higher in patients aged 65 years with mRCC who experience AEs commonly associated with sunitinib, sorafenib, bevacizumab, and pazopanib. Efforts to prevent and/or better manage these events potentially can reduce healthcare costs.