The 67-year-old was diagnosed with the disease a month ago according to Leslie Wolff, who called it a 'serious situation'.
Frazier had the misfortune to be born in the same era as arch-rival Muhammed Ali, although each man's legacy was sealed by their remarkable trilogy.
The Phildephia brawler was the first man to beat Ali in 1971 when he knocked him down before claiming a points verdict in the first defence of his world title.
'Smokin Joe' went on to lose their next two fights though, including the famous 'Thrilla in Manila' that saw Frazier retire on his stool prior to the final round of an epic slugfest.
Frazier also lost twice to the fearsome George Foreman before retiring, although he made a brief and an ill-advised return to the ring in 1981.
He despised Ali for many years for the way he was treated by 'The Greatest' but the pair mellowed and were reconciled in recent times.
Leading British promoter Frank Warren said: "I was very sad to hear the news, it's a tragedy.
"He's one of the greatest fighters of his generation and one of the best heavyweights in history. It's a sad thing and I know everyone in boxing will be wishing him well.
"He beat Ali once and was part of a great era, probably the best heavyweight era."