Given that exercise in moderation reduces cancer risk, I find this take a bit odd. There are plenty of environmental problems that only fit women would be highly exposed to. I.e. due to demographic differences in sport popularity, a fit male is less likely to spend significant time on a synthetic yoga mat in a generally high pollutant indoor environment with a high breathing rate.

Moderation being the keyword, a marathon is definitionally about doing more than moderate exercise

There's a lot of body stress on repairing, maintaining and improving endurance

Maybe that skyrockets cellular division which would maybe would explain some of the impact?