Amy Robach, an anchor on ABC’s “Good Morning America,” had avoided her doctor’s recommendation for a mammogram screening for a year, when a producer for the show called at the end of September and asked her to consider undergoing a televised mammogram.

Reluctantly, she agreed. “You know what, Amy,” her colleague Robin Roberts, a breast cancer survivor, told her, “if one life is saved because of early detection, it’s all worth it.”

On Oct. 1, as all the major television networks promoted the beginning of Breast Cancer Awareness Month, Ms. Robach submitted to the screening live on the show. A television camera discreetly showed the procedure. Normally, these morning-show segments end there. But unbeknown to viewers, the mammogram turned up evidence of cancer. On Monday Ms. Robach announced on “Good Morning America” that she would undergo a double mastectomy later this week.

“While everyone who gets cancer is clearly unlucky, I got lucky by catching it early, and there are so many people to thank for making sure I did,” Ms. Robach, 40, wrote in an ABC blog post that accompanied her announcement. “Every producer, every person who urged me to do this, changed my trajectory. The doctors told me bluntly, ‘That mammogram just saved your life.’ ”