Mayor Rob Ford has been diagnosed with a rare and "very serious" type of malignant tumour called a liposarcoma, according to Zane Cohen, the doctor overseeing Mr. Ford's care at Mount Sinai Hospital in Toronto.

What is liposarcoma?

Liposarcomas arise in fatty tissue, not in organs. Soft-tissue sarcomas – of which liposarcomas are one kind – account for about 1 per cent of all cancers. "Liposarcomas actually make up about 20 per cent of those soft-tissue sarcomas, so it's quite rare," said Prithwish De, an epidemiologist with the Canadian Cancer Society. Canada had 1,175 new cases of soft-tissue sarcoma in 2010, and 471 Canadians died of the disease in 2009, the last years for which statistics are available.

Where is Mr. Ford's tumour? How large is it?

The tumour is in the fatty tissue of the lower left quadrant of his abdomen. The primary tumour is 12 centimetres by 12 centimetres, according to Dr. Cohen.

How aggressive is it?

Dr. Cohen said the tumour appears to be "fairly aggressive." This type of tumour is often slow-growing, Dr. Cohen said, but no evidence of such a mass was found when Mr. Ford had a CT scan in 2011 in relation to a kidney stone.

Has the cancer spread?

Yes. Doctors have found a two-centimetre nodule in the mayor's buttock, behind his left hip. It is not attached to the primary tumour, Dr. Cohen said.

At what "stage" is the cancer?

Dr. Cohen declined to answer that question. Cancers are generally ranked from stages I to IV, with IV being the most serious and usually indicating spread to a major organ. Malcolm Moore, the head of medical oncology and the physician-in-chief at the Princess Margaret Cancer Centre in Toronto, said it is difficult to define the stage based on the information from the news conference. "You can, with some cancers, get what's called a satellite metastastis, where you get a spread that's fairly close to the original tumour," Dr. Moore said. "That generally has a less-ominous implication than if it had spread to the lungs or the liver."

What causes liposarcoma?

There are few known risk factors for soft-cell sarcomas. Lifestyle issues, such as diet and exercise, are not among them. The most common risk factor is radiation treatment for previous cancer, which does not apply in Mr. Ford's case. "Other than just bad luck, there really is no explanation for why this would occur," Dr. Moore said. No regularly recommended test could have caught the tumour earlier. "The difficulty with sarcoma is that it's such a rare tumour, there aren't really effective screening strategies," said Glenn Bauman, the chair of the department of oncology at the school of medicine and dentistry at the University of Western Ontario in London.

What treatment will Mr. Ford undergo?

The mayor will begin his first round of chemotherapy in the next 48 hours. The plan, Dr. Cohen said, is three days of chemotherapy at Mount Sinai followed by 18 days to recover at home. He will then have a second round of chemotherapy and recovery, after which doctors will scan his body to see if the tumour has shrunk. Depending on the results, the medical team could recommend radiation or surgery.

What is the prognosis?

Dr. Cohen said he is "optimistic." The type of tumour Mr. Ford has is generally more sensitive to chemotherapy than others. But Dr. Cohen would not give a long-term prognosis. "The overall [five-year] survival for all soft-tissue sarcomas, including liposarcomas, is 65 per cent," said Dr. Deof the Canadian Cancer Society. "But of course the survival rate depends on the stage the sarcoma is diagnosed at. The survival drops off quite dramatically after stage II cancer."