Katie Herwig was just 26 years old when a bump on her back started bothering her. She scheduled an appointment with her doctor, who removed it and sent it for a biopsy.

After the doctor asked her to come in to discuss the results, Katie learned that she had stage III melanoma.

“I couldn’t stop crying. It was the worst news I could imagine,” says Katie, who was 22 weeks pregnant with her first child at the time. She now had...