The generic cancer prevention advice is to exercise, maintain healthy weight, eat right, etc. It’s really more nuanced that than. Take for example, estrogen positive breast cancers. Being a little overweight actually REDUCES breast cancer risk of an estrogen positive breast cancer if a woman is premenopausal. Then once you hit menopause, you need to lean up fast because being overweight now INCREASES your risk of an estrogen positive breast cancer. Other subtypes of breast cancer don’t follow this pattern.