The main driver for EU-US medical tourism is the much weaker regulation in the US. In the best case, people from the EU travel to the US for innovative new treatments that aren't yet available in the EU; more often, they're suckered into paying huge amounts of money for quackery.

https://en.wikipedia.org/wiki/Burzynski_Clinic

The US has a similar relationship with Mexico; there are a string of clinics along the Mexican border offering unproven cancer treatments that would be difficult or impossible to market under US regulations.

https://en.wikipedia.org/wiki/Clinica_0-19