Before I was diagnosed with testicular cancer at age 21 last year, I only did self-checks in the shower when I remembered to. That translated to about once every two or three months. I knew that the disease usually occurred in younger men, but I also thought I’d felt a lump a few years earlier, and it turned out to be normal.

The lump I found on my right testicle in February 2017 seemed pretty big to me, so it must have formed...