My melanoma diagnosis started out like many others: a suspicious mole followed by a dermatology appointment — and then, bad news. That was in early 2017.

In my case, the mole was on top of my head. And though it darkened and bled occasionally, I still didn’t give it much thought, because I never imagined it might be cancer. I didn’t see a doctor until several months after it first appeared, and even then, only because my wife urged...