I'm not intimately familiar with the data, but results hold among multiple studies that, controlled for age, lifestyle, occupation, and just about any other parameter anyone ever controls for, athletes have lower rates of cancer, and professional athletes have significantly lower rates of cancer (although, that makes "occupation" a variable you can't control for, and it's hard to isolate many other factors, because e.g. those people almost never smoke, and almost always eat healthy. But as much as can be controlled, it seems like sport confers an advantage against cancer, despite subjecting a lot of tissues to repeating and continuous damage).

Statistics is confusing though.

It's possible that people who are less likely to get cancer (for whatever reason) are more likely to be better at sports, thus more likely to be pro athletes; and with the right base rates, it might mean that pro athletes are more likely to not get cancer BECAUSE people who are less likely to get cancer are often athletes. No study that I'm aware of ever tried that angle, and I'm not sure anyone ever collected the right data to try.