OTTAWA — Mayor Rob Ford of Toronto will soon undergo chemotherapy for treatment of two unusual, malignant tumors, a physician told reporters on Wednesday.

Mr. Ford, who has confessed to using crack cocaine and to having bouts of uncontrolled drunkenness, abandoned his re-election campaign last week after being admitted to a hospital. Doug Ford, his eldest brother, has since replaced him on the mayoral ballot, and Rob Ford is seeking election to the City Council.

Dr. Zane Cohen, a colorectal surgeon at Mount Sinai Hospital in Toronto, told a televised news conference that Mr. Ford had been diagnosed with a “fairly aggressive” and rare form of liposarcoma. Dr. Cohen said that he was optimistic that the mayor could be treated successfully, adding that Mr. Ford was “a strong person.”

Yet he also said that the rarity of the cancer made it impossible for him to predict the chances of a full recovery. The mayor, Dr. Cohen said, has a “very rare tumor, and a very difficult tumor.”