Never really understood this argument, as aging is a risk factor for practically every form of malignancy. Less aging = less malignancy.
It would still be fantastic improvement to have the body of a 25-year-old for all my adult years even if my lifespan didn’t change — but while I assume [0] it would extend life expectancy, preventing aging isn’t enough by itself to prevent all illnesses.
[0] I am not involved in medicine or biology and this would be way outside my area even if I had gone down that path, so my knowledge is “watched documentaries” level
If you could hold the probability at the level of an 18 year old, that would massively reduce the incidence.