evidence: Various experts also told us that it is unlikely that residual DNA in the vaccines could integrate into DNA or cause cancer, even in theory. And as we have previously written, there isn’t evidence to date that the vaccines cause cancer or have led to an increase in cancer. [...] The limits are based on the theoretical concern that residual DNA — specifically from mammalian cell lines — could cause cancer or a viral infection, particularly if there were a cancer-causing gene or certain viral DNA present in the cell line. But Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, told us that regulatory limits on residual DNA in vaccines are set conservatively. [...] As we’ve said, social media posts misleadingly refer to the presence of "SV40, a cancer causing sequence." This brings to mind past concerns, which were not borne out, that contamination of polio vaccines with the entire SV40 virus could cause cancer. Researchers discovered in 1960 that monkey kidney cells that had been used to produce some polio vaccines were contaminated with SV40, which was found to cause cancer in rodents. But the virus has not been shown to cause cancer in humans, and the contamination did not ultimately lead to more cancer in children who received the contaminated vaccines compared with those who didn’t.