The aggressive form of cancer Toronto Mayor Rob Ford is battling is typically treated with a minimum of four rounds of chemotherapy and a maximum of six before the tumour is reassessed with a scan, a U.S. oncologist says.

The mayor has undergone two rounds of chemotherapy at Toronto's Mount Sinai Hospital and a third round is scheduled for Monday. Ford told reporters on Friday that the tumour had neither grown in size nor shrunk.

“It’s hard to know what that means, especially after only two rounds of chemotherapy,” said Dr. Robert Canter, a surgical oncologist and associate professor of surgery at the UC Davis Cancer Center in Sacramento, Calif.

"A scan mostly gives doctors a look at the tumour’s size. Although that’s the best sign of response, it’s not a clear picture of the biology of the tumour,” Canter told CBC News.

Sarcomas are found in about one per cent of the adult population, Canter said. Ford's cancer, called pleomorphic liposarcoma, is very rare, representing "a fraction of a fraction" of cases, Canter said, adding that it's usually found "in the extremities" — areas such as the thigh, groin, or behind the knee.

A Toronto Sun story published Friday quoted Ford as saying he's on a "a heavy dose" of antibiotics for pneumonia while he awaits his next round of chemo.

The cancer diagnosis forced Ford to withdraw from the mayor's race last month. Instead, he won a council seat in the northwest Toronto ward currently held by his brother, Doug, who ran for mayor and finished second to John Tory.

Tory will be officially sworn in in December.

Dr. Andrew Wagner, who practises medical oncology in Boston, said chemotherapy could stop Ford's tumour from getting bigger or it could shrink it. He said the pleomorphic liposarcoma Ford has is not considered that large.

“You can see tumours 40 centimetres in size that are operable,” said Wagner, who is with the Sarcoma and Bone Cancer Treatment Center at the Dana-Farber/Brigham and Women's Cancer Center in Boston.

Ford’s tumour, in his abdomen, is 12 centimetres long and wide, roughly the size of a grapefruit.

Neither U.S. doctor has any direct connection to the Ford case, but both said surgery is the mayor's best chance of making a complete recovery.

“Surgery is the only known curative therapy,” Wagner said, adding that stabilizing the tumour can bring about the same survival benefit as shrinking it.

According to the Liddy Shriver Sarcoma Initiative, the five-year survival rate in pleomorphic liposarcoma patients is 56 per cent, while the 10-year survival rate is 39 per cent. The Canadian Cancer Association says the five-year relative survival rate for all soft tissue sarcoma is 65 per cent.

Location more important than size

Doctors say location is usually more important than size when deciding whether a tumour is operable. Surgery could be ruled out, for example, if the mass is too close to the spinal cord, interfering with vital nerves or blood vessels, or sitting on top of the kidneys — although one kidney, in theory, could be removed to gain safe access to the tumour.

Mount Sinai’s public relations office said there was no one available Friday to talk about how many cycles of chemotherapy may be planned for Ford, 45, or what kind of chemotherapy has already been administered.

Wagner said chemotherapy can liquefy cancer cells, leaving the tumour “like a balloon,” without necessarily shrinking it. However, the dead parts of the tumour would be softer, providing relief from symptoms.

Ford's family said the mayor had complained of pain in his abdominal region for about three months before he was taken to hospital on Sept. 10 and that the pain had become “unbearable” the day he was admitted.

Canter said doctors will have to determine the maximal dose of chemotherapy, meaning the largest quantity of a drug a patient can safely take within a given period — how much Ford can tolerate without too many side effects.

He added “there’s a higher threshold” for approving surgery to remove a liposarcoma if it has been found in a second site, because there would be a higher risk that the cancer has spread to even more areas.

Last month, Dr. Zane Cohen, the man leading Ford's medical team, told reporters doctors had also found a "small nodule" in Ford's buttock, behind his left hip, and that it's part of the same tumour discovered earlier. It is about two centimetres in size.