If you had told me years ago that one day all I’d be doing was preventive medicine — and it would all be related to cancer — I’d have said you were crazy. I am not an oncologist. My board certification is in family medicine.

Still, when I was offered the position of medical director at MD Anderson’s Lyda Hill Cancer Prevention Center in 1996, I accepted. It was such a new field then that I appreciated the challenge. But I thought...