Fun fact! Cuba has a vaccine for lung cancer - yes, it works and has been independently verified. No, you can't have it because embargo.
EDIT: vaccine here isn't actually what I thought. In this case it is a treatment to be used for certain kinds of lung cancer, not a preventative measure as we are used to thinking of Vaccine. Thanks to the comment below for going through it and pushing me to do proper research.
While my initial take was a glib link to a wikipedia page and not thoroughly researched, I do sill believe that the embargo has directly caused this treatment to come to market in the west as the levels of cooperation are non-existent. It has been used for 7 years in Cuba but is only now entering Stage 3 trials in the US.
Slight correction on that vaccine, the FDA doesn't authorize any drug for sale in the US that hasn't passed it's rigorous trials and gone through its approval process. It's currently being tested and has more trials ongoing right now. FDA will be able to approve it for sale if it passes its trials.
Also the word cancer vaccine kind of implies cure to some, but it's not by any means:
"MST was 10.83 months for vaccinated vs. 8.86 months for non-vaccinated. In the Phase III trial, the 5-year survival rate was 14.4% for vaccinated subjects vs. 7.9% for controls."
So it might be a useful tool but just don't want to get hopes up unnecessarily. People who's immune system reacted to the vaccine the strongest did best, so current trials are focused on combining it with an immune checkpoint inhibitor drug to increase the immune response even more hopefully (and those drugs are already being used by themselves in cancer). These drugs block "checkpoints" in the immune system that would normally stop it from attacking things like yourself, which we kind of want it to do in cancer.
Not saying I support an embargo in Cuba, I don't, just don't want this comment to be inadvertently read as "Cuba has had the cure to lung cancer this whole time and you're not allowed to have it!" which isn't true.
It's also not a vaccine in the sense it's preventing cancer, it's for the treatment of cancer that is already there, specifically non small cell lung cancers (though it's being tested in other cancers that use the signaling mechanism being targeted). Not saying it's impossible that it could prevent cancer, just that it hasn't been tested in that way to the best of my knowledge.
There is some precedence for a vaccine like that though. The HPV vaccine for instance prevents HPV (and therefore hpv related cancers), but is also used as a treatment if an HPV related cancer develops.