Cancer vaccines aren't unheard of or completely crazy - there's a Glioblastoma (GBM) cancer vaccine that's pretty far in development by Canadian bio VBI Vaccines that may see approval soon, upon completion of their phase 3.
https://en.wikipedia.org/wiki/HPV_vaccine "It is estimated that HPV vaccines may prevent 70% of cervical cancer, 80% of anal cancer, 60% of vaginal cancer, 40% of vulvar cancer, and show more than 90% efficacy in preventing HPV-positive oropharyngeal cancers."