Quality, Cost, and Timeliness of Cancer Treatment in Medicare Advantage and Traditional Medicare.

Importance: Use of Medicare Advantage (MA) insurance has been associated with lower cancer treatment costs than traditional Medicare (TM). Whether there are differences in guideline-concordant care or treatment costs for beneficiaries insured under MA vs TM is unknown. Objective: To assess whether Medicare insurance type is associated with receipt of optimal cancer treatment and costs. Design, Setting, and Participants: Retrospective cohort study of a population-based sample using Medicare claims and encounter data from 2015 through 2019. Participants were Medicare beneficiaries with continuous enrollment in either MA or TM and an incident cancer diagnosis from 2016 through 2019. Included patients were those with cancer treatment scenarios (eg, metastatic melanoma, adjuvant therapy for stage III colon cancer) that had substantial variation in the costs of recommended treatment options. Data were analyzed from April 2025 to March 2026. Exposures: Medicare insurance type of MA or TM. Main Outcomes and Measures: The pharmacologic cancer treatment among the available options each patient initiated was analyzed using Medicare data. Each patient's treatment was linked by diagnosis date to contemporary National Comprehensive Cancer Network Guidelines recommendations and Medicare reimbursement rates to ascertain the coprimary outcomes whether a patient received the optimal treatment for their cancer type and the anticipated cost of the initiated treatment. The association of outcomes with insurance type was accessed using generalized estimating equations to estimate risk ratios (RRs) after balancing patient characteristics through inverse probability-of-treatment weighting. Models were clustered at the physician level and adjusted for scenario, diagnosis year, scenario × diagnosis year interaction, and oncologist characteristics. Results: Of 35 245 patients (median age, 74 [IQR 70-79] years; 63.2% male), 24 269 had TM and 10 976 had MA. The median time to treatment initiation was 36 (IQR, 20-60) days for MA vs 35 (IQR, 19-59) days for TM. The unadjusted mean (SD) treatment cost was $29 252 ($80 391) for MA vs $40 874 ($106 205) for TM. MA beneficiaries had a likelihood of optimal treatment similar to TM beneficiaries (adjusted RR, 0.99; 95% CI, 0.97-1.02), and MA was associated with lower treatment cost (adjusted cost ratio, 0.94; 95% CI, 0.91- 0.97). Mean savings within this patient cohort was -$931 (95% CI, -$1244 to -$615). Conclusions and Relevance: In this cohort study of Medicare beneficiaries with cancer, MA beneficiaries had lower estimated treatment costs and similar likelihood of receiving optimal treatment compared with TM beneficiaries.