Toronto Mayor Rob Ford is suffering from a rare and difficult cancer that will require aggressive chemotherapy, his doctor said Wednesday.

Dr. Zane Cohen, a colorectal surgeon at Mount Sinai hospital, said Ford has a malignant sarcoma. Ford has been hospitalized for a week with a tumor in his abdomen.

Cohen said mayor will undergo chemotherapy within the next two days and that he will be treated with fairly intensive chemotherapeutic agents.  He said the cancer is spreading and that they have found "a small nodule in the buttock" near the left hip.

The mayor withdrew his re-election bid Friday as he undergoes treatment, dramatically ending a campaign he had doggedly pursued despite calls for him to quit amid drug and alcohol scandals and a stint in rehab.

Doug Ford is running for mayor in his brother's place. The mayor's family was not with the doctor when the update was provided.

The mayor checked himself into a hospital last week after complaining of stomach pain while eating breakfast with his brother.

"He's having some pain still," Cohen said. "We are managing that."

He said the initial biopsy came back inconclusive but said a second biopsy led them to conclusive diagnosis.

Doug Ford Sr., the mayor's farther, died of colon cancer in 2006.

Ford, 45, gained international notoriety last year when the Toronto Star and the U.S. website Gawker reported the existence of a video apparently showing the mayor inhaling from a crack pipe. He denied the existence of the video for months but finally admitted to using crack in a "drunken stupor" after police announced they had obtained a copy.  When reports emerged this year of a second video showing him apparently smoking crack, Ford entered rehab for two months and returned to work and campaigning in June.

The Fords announced last week that Doug Ford will now run for mayor and Rob will seek a City Council seat representing a district in his home suburb of Etobicoke. Doug Ford hasn't started campaigning for the Oct. 27 election since he announced he would run for mayor.

Olivia Chow, who is running to replace Ford, said wished Ford and his family well and said she knows Rob is strong.

"Since he's so strong and he's such a good fighter I hope he can win this battle," Chow, who is a cancer survivor.

John Tory, the leading candidate, called Ford a fighter who should know the people of Toronto will be standing behind him