Medigap Protection and Plan Switching Among Medicare Advantage Enrollees With Cancer.

Importance: An increasing number of Medicare beneficiaries with cancer report Medicare Advantage (MA) coverage, but certain features of MA (eg, utilization management) may impede access to cancer care. MA beneficiaries may desire to switch to traditional Medicare (TM), which imposes little to no utilization restrictions, but switching may be challenging because access to Medigap-providing financial protections against high cost sharing in TM-is limited by medical underwriting of beneficiaries applying after initial Medicare enrollment in most states. Objective: To examine associations of Medigap guaranteed issue protections that prohibit medical underwriting with MA disenrollment among beneficiaries newly diagnosed with cancer. Design, Setting, and Participants: This retrospective cohort study examined Medicare beneficiaries 69 years and older who were newly diagnosed with cancer from 2014 to 2019 in the Surveillance, Epidemiology, and End Results Program-linked Medicare database. Beneficiaries continuously enrolled in Medicare Parts A and B for 4 years before to 1 year after diagnosis were included. Data were analyzed from October 2024 to April 2025. Exposure: A new cancer diagnosis. Main Outcomes and Measures: The outcome was switching to TM. Among those who were initially enrolled in MA, a difference-in-differences design was implemented to compare changes in the probability of MA disenrollment between beneficiaries diagnosed in 3 guaranteed issue states (New York, Connecticut, and Massachusetts) vs other 13 states contributing to the Surveillance, Epidemiology, and End Results Program registry, before and after diagnosis. Results: The study included 180 057 MA beneficiaries 69 years and older who were newly diagnosed with cancer (44.5% diagnosed at age 69-75 years; 51.5% male; 8.0% Hispanic; 7.4% non-Hispanic Black; 78.5% non-Hispanic White; and 6.1% another or unknown race and ethnicity). The rate of switching in guaranteed issue states increased from 2.1% to 4.7% following diagnosis but remained unchanged in other states (1.8% to 1.7%), corresponding to a difference-in-differences of 2.5 percentage points (95% CI, 1.9-3.2 percentage points; P < .001), or a 120% relative change. This differential increase was concentrated among beneficiaries who were younger, non-Hispanic White, diagnosed with distant-stage or rarer cancers, or enrolled in plans with more generous coverage (eg, PPO plans) or lower plan star ratings. Conclusions and Relevance: In this cohort study, state Medigap guaranteed issue protections were associated with higher rates of switching to TM among MA beneficiaries newly diagnosed with cancer. These findings underscore the protective association of state Medigap regulations in facilitating a switch to TM (especially among beneficiaries who likely desired more flexibility in accessing and receiving care) and illuminate potential disparities in switching that may reflect unequal abilities to compare and afford plans.