She'll undergo reconstructive surgery over the next eight months.
"I'm going to have cute boobs 'til I'm 90, so there's that," she joked in the interview, which aired Tuesday. "I'll have the best boobs in the nursing home. I'll be the envy of all the ladies around the bridge table…"
… Applegate's cancer was detected early through a doctor-ordered MRI. She said she's starting a program to help women at high risk for breast cancer to meet the costs of an MRI, which is not always covered by insurance.
The news of breast cancer initially shook her up, she said.
"I was so mad," she told "Good Morning America." "I was just shaking and -- and then also immediately, I had to go into ... 'take-care-of-business-mode,' which was ... I asked them, 'What do I do now? What -- what is it that I do? I get a doctor, I get a surgeon, I get an oncologist? What do I do?' "
The actress said she quickly made appointments, and also changed her diet to one consisting of fish, grains, beans and vegetables, avoiding processed foods.