Sarah Rykowski is a chief prosecutor in the U.S. Army. In 2013, while stationed in Seoul, South Korea, she discovered a lump close to her armpit during a breast self-exam.

As the daughter of a registered nurse, Sarah knew she should see a doctor at her next post in Oklahoma. There, a mammogram and biopsy revealed early-stage invasive ductal carcinoma, a form of breast cancer. It begins in the milk ducts and can spread through the...