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.