This is a false claim. I say that simply because there is no scientific evidence that mRNA vaccines cause cancer. Also, this claim has no sources except for posts on "X" or what was formally known as Twitter. When looking up connections between cancer and mRNA vaccines, I found multiple sources that explain why this is a false claim. An article in the Daily Herald titled, "Facts Matter: Biden's Cancer Not Caused by Vaccines," mentions how after Biden's diagnosis, social media users began speculating that his cancer was caused by Covid-19 vaccines. However, the article mentions how these claims are false and uses Politifact as a reference using the quote from a molecular biologist that, "in order to cause cancer, something has to damage DNA or cause chronic damage that leads to more mistakes in DNA replication. Neither mRNA nor the spike protein it produces have any capability to mutate DNA.” When looking that the article in Politifact, it is mentioned that, " cancer rates have not increased in an unexpected way, which you would definitely expect to see if the mass rollout of a cancer-causing vaccine just happened." This affirms the fact that there has been no evidence that vaccines cause cancer as there have been no affect on cancer rates following the distribution of Covid vaccines. When looking at information from the Global Vaccine Data Network, vaccines are actually, "one of the most successful tools in preventing virus-related cancers." Looking into the mRNA vaccine specifically, the Global Vaccine Data Network states that mRNA vaccines don't, "contain live virus or long-lived genetic material capable of altering cellular DNA. Thus, there is no plausible mechanism by which mRNA vaccines could cause cancer." After looking at these sources, there is no scientific evidence that Biden's cancer was cause by mRNA vaccines as claimed on social media.
https://www.dailyherald.com/20250525/news/facts-matter-bidens-cancer-not-caused-by-vaccines/
https://www.politifact.com/factchecks/2025/may/20/tweets/Biden-turbo-cancer-vaccine-covid-mrna/
https://globalvaccinedatanetwork.org/news/turbo_cancer_and_mrna_myth_that_defies_biology_and_physics