Story highlights Rob Ford decided not to run for re-election after his tumor was discovered

The controversial mayor has a rare cancer, which has spread from his abdomen

Doctor is unsure about the prognosis, but treatment will start with chemo

Ford returned to work in late June after two months in rehab

Toronto Mayor Rob Ford soon will begin chemotherapy to treat a rare and aggressive cancer, a doctor at Mount Sinai Hospital in the city said Wednesday.

Dr. Zane Cohen said Ford has a malignant liposarcoma, and a second biopsy on his tumor done Monday shows it is aggressive.

"However, we are optimistic about this tumor," Cohen said.

Ford, who recently announced he will not run for re-election, will start chemotherapy by Friday afternoon.

The cancer has spread from the fatty tissue of Ford's abdomen to other parts of his body, including his buttocks, Cohen said.

The doctor added that this type of tumor comprises only about 1% of all cancers and has at least 60 different types of cells, making it difficult to treat.

Cohen said there would be 18 days in between chemo and there would be another 18-day break, after which doctors would reassess Ford's treatment plan.

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Those three-day rounds of chemotherapy might eventually be followed by surgery, radiation or both, he said.

The health ailment adds to the list of struggles facing Ford, whose fall from grace began in May 2013 with the release of a cell phone video that appeared to show him smoking crack cocaine. The Toronto city council largely stripped him of his mayoral powers months later over those and other allegations of bad behavior.

Ford didn't back down, though, instead vowing "outright war" on the city council.

The mayor apologized for "a lot of stupid things," including having used crack cocaine, but he refused to resign or enter rehab. In fact, despite all the criticism and his becoming a punchline for jokes in Canada as well as the United States, Ford launched a bid for re-election.

This past spring, after a local newspaper reported on a new video that allegedly showed him smoking crack cocaine, Ford relented on one front: by going into rehab.

He returned to work in late June, after a two-month rehab stint, saying he was "ashamed, embarrassed and humiliated" by some of his past actions.

But he refused to resign or refrain from campaigning, saying to the voters of Toronto, "I look forward to serving you for many, many more years."

Ford's term officially ends December 1.

When he announced his decision not to seek re-election last week, Ford has asked his brother, Doug Ford, to run for mayor in the October 27 balloting.

Doug Ford released a statement Wednesday on behalf of the Ford family saying of his brother's diagnosis: "I can't begin to share how devastating this has been for Rob and our family."

"Rob has always been so strong for all of us and now I ask us all to be strong for him," Doug Ford said in the statement, adding, "Rob will beat this."