Rob Ford has been diagnosed with a rare form of cancer that will require chemotherapy and possible radiation treatment or surgery.

"The diagnosis is a malignant liposarcoma," said Dr. Zane Cohen, an expert in colon and rectal surgery at Mount Sinai Hospital, who is leading the team caring for the mayor. "It arises from the soft tissue structures ... it has sixty different cell types, and that's what makes it a very rare tumour and a very difficult tumour, however we are optimistic about this tumour."

Cohen said the cancerous mass, which is about 12 cms in size, is located in the fatty tissue of the mayor's abdomen. A smaller, 2 cm nodule was found "in the buttock behind the left hip."

"We think it's a fairly aggressive tumour," Cohen said. He told reporters that the mayor will undergo three days of chemotherapy followed by a "wash out" period of 18 days, after which he will be temporarily discharged before receiving a second round of treatment. Despite the aggressive nature of the tumour, Cohen said he was confident in the hospital's treatment plan.

"I think he will have more good days than bad."

Ford was first hospitalized last week after complaining of abdominal pain. A subsequent CT scan at Humber River Hospital revealed the presence of a tumour, and Ford was transferred to Mount Sinai Hospital for further treatment and a biopsy.

The mayor quit his re-election bid a day after moving downtown, allowing Doug Ford to take his place on the ballot Friday, moments before the 2 p.m. registration deadline. Rob said he would run for city councillor in Ward 2 against popular candidate Andray Domise instead.

"I can't begin to share how devastating this has been for Rob and our family," said Doug Ford in a written statement. "He is an incredible husband, father, brother and son and he remains upbeat and determined to fight this ... your kind words and well wishes mean everything to him right now. Rob will beat this."

Prime Minister Stephen Harper issued a statement following news of the diagnosis. "The thoughts and prayers of all Canadians are with Mr. Ford and his family at this difficult time. We wish him a speedy and complete recovery and are certain that he will take on this fight with all of his characteristic tenacity and energy."

Ford was treated for appendicitis in 2009. In office, Ford was hospitalized with kidney stones in 2011 and a throat problem that aggravated his asthma in 2012. Liposarcomas, which comprise about one percent of all cancers, are not associated with organs and often develop within "muscles, tendons, connective tissue, fat, blood vessels, nerves, and joint tissue," according to the Mount Sinai Hospital website. "The exact cause of soft tissue sarcoma is not known."

The Toronto Sun reported on Tuesday that Ford had been handling a limited amount of paperwork from his bed. "I'm feeling pretty sick," he told confidant Joe Warmington. "You have got to carry on."

Despite being present at the hospital, Ford's brothers Doug and Randy, mother Diane, and wife Renata did not appear at the press conference.

It's not clear whether Ford will continue with his bid for councillor in Ward 2 or take a formal leave of absence from city hall.

Chris Bateman is a staff writer at blogTO. Follow him on Twitter at @chrisbateman.

Image: John Tavares/blogTO Flickr pool.