Samantha Harris diagnosed with breast cancer

Samantha Harris was diagnosed with breast cancer, she announced Wednesday on "Good Morning America."

Harris, 40, detected a lump last fall via self-examination and had a clean mammogram. But months later, Harris said, something still felt off and so she consulted a breast cancer specialist several months later. A needle biopsy and a lumpectomy revealed that she did in fact have breast cancer.

"It felt like an elephant was sitting on my chest," Harris told People.

"The realization sort of overtook me, my eyes started to well up from tears when I was trying to keep myself calm because I thought the most important thing ... was that I needed to focus and listen to what they were saying," Harris recounted to Entertainment Tonight.

"It's scary and you worry. ... My daughters are three and six, you know. All they're concerned about is to have mommy active, be able to hold them, hug them, kiss them," a shaken up Harris said. "I want to still do and from what the doctors say, I will still be able to do, but no matter how positive of a diagnosis as I have, it doesn't keep the demons of fear from taking over your mind and your thought process."

The former "Entertainment Tonight" host has opted for a double mastectomy to treat the cancer, instead of a less-radical second lumpectomy with radiation, and will undergo the surgery later this month. Harris told People, "I felt so much calmer" after making a decision.

"I was sick of feeling the way that I did in the days after the diagnosis," Harris added. "I knew I needed to take control."

Harris' former "Dancing with the Stars" co-host Tom Bergeron posted words of support on Twitter: "Join me in sending positive thoughts and prayers to my former @DancingABC co-host @SamanthaHarris as she kicks cancer's ass #standuptocancer."

Harris has long been an advocate for breast cancer awareness and volunteers for charity events such as Feeding America, the Revlon Run/Walk and What A Pair.