Until January 2020, I had always felt like I had an unspoken agreement with cancer: I’d make good lifestyle choices — protecting my skin, avoiding tobacco and exercising regularly — and it would leave me alone.

I thought we had a deal. Because there’s no history of cancer in my family. I’ve never worked in a chemical factory. And, up until last year, I’d gone more than half a century without so much as a peep out of cancer....