The Italian, 54, said he had undergone eight months of chemotherapy and six weeks of radiotherapy.
He said he initially tried to hide his illness, even wearing a sweater under his shirt so nobody would notice the weight loss.
Eventually, he chose to reveal it in a new book, hoping his experience might inspire others to fight.
“I’m fine now, very well indeed,” Vialli told Italian newspaper Corriere della Sera.
“It’s been a year and I’m back to having a strong physique. But I still have no certainty of how this match will end.”
Vialli, who now works for Sky Sport Italia as a pundit, was one of the biggest stars of his generation.
He won the Serie A and the Champions League with the Italian powerhouse Juventus before signing for Chelsea in 1996.
Vialli won the FA Cup as a player at Stamford Bridge and was named player-manager following the sacking of Ruud Gullit in February 1998 – leading the Blues to victory in the League Cup, UEFA Cup Winners’ Cup and UEFA Super Cup the same year.
Chelsea sent Vialli well-wishes in a tweet, saying; “We love this guy. Best wishes from all of us at Chelsea to Gianluca Vialli. We’re all thinking of you, Luca.”
In the interview, Vialli said the disease initially gave him a sense of shame.
“I knew it was going to be hard to have to tell others, to tell my family. You would never want to hurt the people who love you”, he said.
“If gives you a sense of shame, as if it is your fault. I would wear a sweater under my shirt so others did not notice anything, that I would still be the Vialli they knew.”
Eventually, he said, he came to consider it “a phase of my life that had to be lived with courage and from which to learn something”.
He added: “Life is 10% what happens to us, 90% how we face up to it.
“I hope my story can inspire other people at difficult times in their life.”
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Vialli made 59 appearances for Italy, and was part of the team that reached the World Cup semi-finals in 1990.
With Chelsea, he led the team to victory in the 2000 FA Cup final and Charity Shield, but was sacked the following season.