Lee, 48, told "GMA" co-anchor Robin Roberts, who is herself a breast cancer survivor, about the moment she got the news. She said she was doing a photo shoot for the Most Beautiful issue of People magazine on March 27.
"And I walked off the set, and 20 minutes later my doctor called and told me I had breast cancer," she said. "I didn't even cry, I was stunned … You know, and that's just how fast life turns. It turns on a dime."
The lifestyle guru is best known for her television shows -- including "Semi-Homemade Cooking with Sandra Lee," multiple cookbooks and a magazine.
Lee told Roberts about her treatment plan. The interview was recorded on Friday but aired on "GMA" today.
"When the lumpectomy was done, they did not have clean margins. And so I went back to my radiologist," who told her she would have daily radiation for six to eight weeks, she said.
They also told suggested that she have a mastectomy.
"And so I said, 'OK. If I'm going to have a mastectomy, am I supposed to just get one done?' Both the radiologist and the doctor said, 'You're a ticking time bomb.' And they both said, 'You need -- I would just get them both done,'" Lee recalled.
When Roberts asked how Cuomo handled the news, Lee replied: "Well, he was -- after I called my sister, he was the next call. I think he was as stunned as I was."
She said Cuomo, 57, has been "extremely supportive."
"He's going to be in the operating room with me," she said.
In a statement released today by the governor’s office, Cuomo said he was "devastated" by the news, but thankful Lee’s cancer was detected in the early stages, and he will be there to support her.
"A situation like this quickly puts life in the proper perspective and reminds one of what’s truly important. To that end, I expect to take some personal time because I want to be with Sandy to support her in any way I can as she handles the trauma of her operation and the pain of the recovery,” he said. “For those of you familiar with Sandy’s life story it will not surprise you that she has met this latest challenge with determination, resolve and grace."
Lee said there were two ways that cancer takes a toll.
"It beats up your body, and it beats you up emotionally. And it -- I wasn't going let it rob me from one day of happiness," she said.
Lee said her immediate goal is to have the surgery and recover. After that, she says, she's going make sure that her siblings and nieces are screened.
Not all organizations agree on the guidelines for when women should have mammograms. Some groups recommend that women start to have screenings when they turn 40, while others recommend women start when they are 50.
Roberts asked Lee whether she was having regular checkups, and Lee said the cancer was detected from "a normal mammogram."
She added: "I'm 48 years old. I've got -- I've got a couple years till 50 ... If I would have waited, I probably wouldn't even be sitting here. And if you would have waited--"
Roberts was diagnosed with breast cancer when she was 46.
Lee said that she was speaking publicly about her diagnosis because she wants younger women -- in their 20s and 30s -- to be aware and not to delay.
"Girls in 20s and their 30s just have to know. And I don't want women to wait. And that's why I'm talking … If it saves one person, and makes one more person go get a mammogram, and if they're sitting down right now watching this, don't watch this TV. Go pick your phone up, and call your doctor and get your rear end in there and get a mammogram right now," she said
"You hear about it and it is always someone else, it's a friend that you sent flowers to and you wish well and that you watch every single day like I watched you. And you were my hero," she said. "But I never thought I would be dealing with this."