My dad’s mother was diagnosed with breast cancer when she was in her 60s. But that was considered pretty normal at the time, so she didn’t have any genetic testing done. That’s why it was such a shock to be diagnosed with breast cancer myself at age 28 in January 2017. As far as I knew, my grandmother and I were the only people in my family who’d ever had cancer.

Because I was so young when I was diagnosed, I got genetic testing...