BACKGROUND: Medicare Advantage (MA) plans may offer more benefits and lower costs relative to Traditional Medicare (TM), but may also provide narrower provider networks and pre-authorization requirements. We explore the impact of a cancer diagnosis on switching between MA and TM after diagnosis. METHODS: We used the 2015-2019 Surveillance, Epidemiology and End Results-Medicare data to examine patterns of switching between MA and TM after cancer relative to those without cancer. We used binomial generalized estimating equations to evaluate the cancer and sociodemographic characteristics of those with higher probabilities of switching. RESULTS: Among those initially enrolled in MA plans (39.27% of those with vs 40.79% without cancer), 3.76% of individuals with cancer switched to TM compared to 2.23% without cancer. For those initially enrolled in TM, 2.96% of individuals with cancer switched to MA vs 4.35% without cancer. Multivariable analyses demonstrated that, among individuals starting in MA, a cancer diagnosis was associated with a 52.02% increase in switching relative to those without cancer, whereas among those starting in TM, a cancer diagnosis was associated with a 26.90% reduction in switching. Younger individuals, males, dual-eligible, those with more comorbidities, rural-dwellers, and those living in zip codes with higher education and income levels also had higher probabilities of switching from MA to TM. CONCLUSIONS: Prior to diagnosis, MA enrollment is comparable between individuals with and without cancer. However, after diagnosis, individuals with cancer have higher probability of switching from MA to TM and lower probability of switching from TM to MA.