evidence: A: There are no known cases, and it’s very unlikely. In the 1950s and 1960s, people did receive polio vaccines contaminated with a virus that causes cancer in rodents. But research suggests this virus doesn’t cause cancer in humans. [...] Many of our readers have asked us whether people have developed cancer because they received the polio vaccine. Facebook users also have flagged stories on this topic as potentially false. The bottom line: It’s highly unlikely that the lots of polio vaccine contaminated in the ‘50s and ‘60s have caused anyone to develop cancer. [...] If the polio vaccine contaminated with SV40 did cause cancer, scientists would expect to see an increased risk of cancer in the population of people who received the vaccine. But just because they didn’t find this effect in the group doesn’t rule out the possibility that some select individuals did develop cancer because of the vaccine.