The model told the panellists: "It’s emotional. We kept it quiet for two and a half years now. The positive news is we caught it early enough."
Singer Rod Stewart revealed in September that he was free from prostate cancer after battling the disease for three years and undergoing two years of secret treatment.
In a video message from New York to the Loose Women viewers, Mr Stewart called on men to get tested for prostate cancer, saying: "Please get down to the doctors and get tested, it's a rotten disease.
He jokingly added: "Finger up the bum, no harm done."
Despite the positive news, Ms Lancaster was emotional when recalling the 'aggressive' prostate cancer diagnosis in 2016 and the struggles they faced during his battle to cure it, as she explained: "It came on really quickly."
"With Rod it was an aggressive one. It left the gland and travelled to the outside tissues."
She continued: "He had a few symptoms. It started moving quite quickly, the results, the numbers. They said it was best we do a rectal exam. It's the only way. A specialist has to do that. And they did find a lump. Then it was like, 'okay we can't ignore this'."
"Then we got the shock news it was cancer, and we looked at the different ways of dealing with it."
She explained the different tests Mr Stewart underwent: "Another scary moment was where we had to have more invasive tests and scans to see if it was anywhere else secondary in his body, which was the most frightening test of all. But it hadn't gone."
She explained they decided to keep the diagnosis from their younger sons Alastair, 13 and Aiden, eight.
The Loose Women panellist said Mr Stewart underwent intensive radiation treatment every single day for three months at a London clinic.
The 78-year-old singer told fans about his secret battle during a fundraising event with former Faces band members Kenney Jones and Ronnie Wood in September.
Ms Lancaster recalled the moment her husband came out with the news: "After a few songs he said: 'Hi everyone, thank you so much for coming and I have to just take this moment, I owe it to everyone, I'm a survivor'."
In July, the 'Rhythm of my Heart' singer was told there was no trace left of the disease, and Ms Lancaster told Little Women viewers he's 'very up on his health' and is doing 'fantastic'.
She added: "He's just done a stint in Vegas, flown to New York for a charity event, and he’s back home on Saturday, there’s no slowing him down!
"He doesn't believe in retirement, he wants to keep going forever, so he's always getting screenings and tests."
Discussing his video message, she explained: "He just wanted to give a message out to all men, especially over 50, you can actually go and request to get a PSA blood test.
"Which will give you a little indication, it's not a sure result. But if there's a sign that the readings are elevated, and if it's the case you can have further examinations rectally, which is an awkward thing for men to talk about.
"Men don't get an offer to come in, you can request it. Really that should change."