The actress, who played Ronnie Mitchell in the popular soap, opened up about her diagnosis as she paid tribute to the late Olivia Newton-John on Twitter.
Samantha explained that the Physical singer had come to see her star as Sandy in Grease in the West End as she shared a throwback photo from the sweet interaction.
“This was the most magical of evenings. Olivia and Chloe had come to see Grease in London and we had dinner together afterwards. I was so excited and in awe, she was my childhood,” the 49-year-old said.
“I now start my own battle with this disease and am left feeling deeply moved.”
Friends and fans flocked to the comments section to send Samantha their well wishes.
Fellow soap star Claire Sweeney wrote: “I’m so sorry and sad to read this Sam. God bless you and your family x”
Samantha’s EastEnders co-star Laurie Brett, who played Jane Beale from 2004 until 2012, said: “Bloody hell Sam, am speechless. Sending you all the love in the world. You got this, and we got you..”
And This Morning’s soap expert Sharon Marshall added: “Wishing you love and strength”
Olivia Newton-John died on Monday morning at the age of 73 after a 30-year battle with breast cancer.
Her husband, John Easterling, confirmed that the British-born singer died “peacefully” at her ranch in Southern California surrounded by family and friends.
Dame Olivia is best known for her starring role as Sandy in the 1978 film Grease, with her co-star John Travolta leading tributes online last night.
Writing on Instagram, Travolta said that her “impact was incredible” and signed off his tribute to the actress as “your Danny”.
“My dearest Olivia, you made all of our lives so much better,” he wrote.
“Your impact was incredible. I love you so much. We will see you down the road and we will all be together again.
“Yours from the first moment I saw you and forever! Your Danny, your John!”
Stockard Channing, who played fellow Pink Lady Betty Rizzo in the film said Dame Olivia was “the essence of summer” in her own tribute.
“I don’t know if I’ve known a lovelier human being,” she said in a statement to US media outlet People.
“Olivia was the essence of summer – her sunniness, her warmth and her grace are what always come to mind when I think of her.
“I will miss her enormously,” she added.