Former 'GMA' host Joan Lunden shares breast cancer diagnosis

NEW YORK (KABC) -- Former "Good Morning America" co-host Joan Lunden returned to the show Tuesday to reveal that she has been diagnosed with breast cancer.

Lunden told Robin Roberts, who is also a breast cancer survivor, that her cancer did not show up in her mammogram. Her cancer was found in a follow-up ultrasound done because she has "dense fibrous tissue."

As a result, Lunden underwent a core biopsy and will undergo chemotherapy, surgery and radiation.

She is expected to make a full recovery.

Lunden co-hosted "GMA" from 1980 to 1997. She later became a health advocate and said her late father, a cancer surgeon, inspired her to come forward.

"I went from being a victim to being empowered and having a purpose," she said on "GMA."

ABC News contributed to this report.