"Cancer does not discriminate," Pickler, 26, said on Wednesday's show.
She and her longtime friend, Summer Holt Miller, had their hair shaved down to the scalp in Nashville Tuesday and the moment was taped by "GMA" cameras. The segment aired Wednesday morning.
Miller, 36, underwent a double mastectomy after she was diagnosed with breast cancer in June. She is to begin chemotherapy this week, E! News said.
"If this compels even one person to change their mentality toward waiting until the age of 40 for their mammogram, then it will be worth it," Miller said.