When my father-in-law was in his 30s, he was diagnosed with colorectal cancer as a result of familial adenomatous polyposis (FAP), a genetic condition that stimulates the production of polyps and increases a person’s cancer risk. My husband, Jesse, learned that he too had familial adenomatous polyposis when he was 15 years old.

By the time I met Jesse in college, he’d already had a colectomy, a procedure that removed his colon....