Comment by AlphaCharlie

not just higher cancer rates, but higher rates of all kinds of aging-related deaths

the advantage of being warm-blooded is that your metabolism is more precise and much faster, but, as james dean quoted willard motley saying, 'live fast, die young'

most of the causes of aging are unwanted chemical reactions; https://www.cell.com/action/showPdf?pii=S0092-8674%2813%2900... is a highly-cited paper reviewing what we knew about the causes of aging 11 years ago. chemical reactions of all kinds follow the https://en.wikipedia.org/wiki/Arrhenius_equation which makes them happen about 2–3 times faster per 10° temperature rise

(being old is a more important risk factor for cancer than anything else i can think of, even smoking and radioactive fallout)

small sharks around greenland, to take an extreme example, are at essentially the temperature of the seawater, about -1.8°. larger sharks could conceivably raise their internal body temperature, but greenland sharks swim very slowly to avoid this even when they are large. so their metabolism is about 16× slower than yours is—both healing and aging processes happen slower. their gestational period is about 8–18 years

Probably constant generation of reactive oxidizing chemicals from the higher metabolism needed to maintain body temperature.