That's true if you try to change from an Advantage plan to a supplement or had original Medicare without signing up for a supplement. In fact, I doubt most (any?) supplemental plan would underwrite you at that point if you had PCa. But if you sign up for a supplement at the time of your initial enrollment in Medicare, there is no underwriting allowed. That's why I chose to go the supplement route with original Medicare from the get go. Plus some states have some limited ability to change supplemental plans down the road. For example, where you live in California, there's a "birthday rule" where you can change plans yearly to a like plan with a different insurance company. Not that great, but at least you're unlikely to be stuck with a single insurer.