The article used in the claim talks about how it is true that Covid vaccines have helped cancer patients live longer. Over half (55.7%) of vaccinated patients were alive compared to the unvaccinated patients in which only 30.7% were still alive after 3 years since starting treatment. Scientists found that pairing an mRNA vaccine with immunotherapy helped active the immune system. It doesn't target just cancer, but it primes the immune system to be more responsive and alert.
I did further research on this topic and found an article by UFHealth that confirms this is true. They also did a study on this and found that receiving a Covid mRNA vaccine within 100 days of starting immunotherapy increased the life of cancer patients significantly.