TORONTO Mayor Rob Ford has a very rare and aggressive type of cancerous tumour in his abdomen, his doctor has said, and the controversial municipal leader will start chemotherapy treatment within days.

Mr Ford, who made international headlines with his admission he smoked crack cocaine while in office, was hospitalised last week after having unbearable abdominal pains. He dropped out of the city's hotly contested mayoral race last week.

Toronto doctor Zane Cohen said the mayor had malignant liposarcoma, a type of cancerous tumour that arises in fat cells in deep soft tissue.

Dr Cohen, a colorectal surgeon Toronto's Mount Sinai Hospital, called it a "very rare" and "very difficult" type of tumour, noting that malignant liposarcoma makes up just one per cent of all cancers. However, he was also optimistic about Mr Ford's treatment prospects.

The surgeon said: "The plan will be, initially, chemotherapy. There may or may not be radiation involved, there may or there may not be surgery involved, it will all depend on the response to the initial treatment, and subsequent treatments as well."

After being admitted to the hospital last week, Mr Ford dropped his bid for re-election as mayor and was replaced by his brother and campaign manager Doug Ford. Doug Ford said the cancer diagnosis was "devastating".