Assume you’re life-lusted and are willing to abandon every moral you have just to live. Paying for cancer treatment is also worth prison time to you.
Also assume you’ve exhausted all ethical fundraising options, i.e. GoFundMe, loans, etc. and that insurance won’t cover treatment for whatever reason.
The thing is that, at least for Americans, their country of origin can treat the cancer as well as any European country, and “I’m too poor to live in my own country” is usually not an accepted reason for immigration or asylum.
There are some countries that have medical treatment visas but those usually require people to pay for the treatment, and while it’s order of magnitude cheaper than US hospitals but for cancer is still not exactly cheap.