Former Toronto Mayor Rob Ford died Tuesday while suffering from a rare type of cancer known as pleomorphic liposarcoma.

Ford endured nine rounds of chemotherapy, his chief of staff Dan Jacobs said, as well as surgery and radiation treatment to stop the spread of cancer that was first diagnosed in September 2014.

Ford, married with two children, died at age 46 at Toronto's Mount Sinai Hospital, surrounded by family members.

What is it?

Mayor Rob Ford releases statement

Rob Ford underwent chemotherapy, radiation and surgery to treat his disease. He never responded to the last round of chemotherapy. (Chris Young/Canadian Press)

Dr. Robert Canter, an associate professor at the University of California Davis School of Medicine in Sacramento, Calif., said liposarcoma is the most common type of sarcoma, which is cancer that comes from the soft tissues, including fat, muscle and cartilage.

Canter is a surgical oncologist with expertise in soft tissue sarcoma. He was speaking with CBCNews.ca on Monday, before Ford's death.

He said liposarcoma has five subtypes. Pleomorphic is one subtype and the rarest, Canter said. The cells of pleomorphic sarcoma are atypical, which means they vary in size and shape. "They are somewhat bizarre," he said.

He said soft tissue sarcoma is a group of malignancies. There are at least 50 to 100 types of soft tissue sarcoma. They are distinct cancers in the ways they respond to treatment.

How is it treated?

Surgery is the most common treatment, but a combination of treatment is often used, Canter said, including chemotherapy, radiation and surgery. 

Rob Ford

Toronto residents are writing messages of support to Ford on a 'get well soon' website while he is in hospital.

If the tumour is isolated or localized, doctors will often treat it with chemotherapy to shrink the tumour to the point where it can be successfully removed. 

"In cases where it's in more than one spot, the prognosis tends to be not nearly as good," he said. "There are risks of progression. It can be a ticking time bomb."

Earlier this month, Doug Ford said his brother had been pursuing targeted chemotherapy at Mount Sinai. 

The treatment involves implanting a piece of tissue from a patient's tumour into mice, which will take about three months to grow in the rodents. Researchers then test different chemotherapy treatments on the mice to see which drugs are most effective in decreasing the size of the tumours. 

"It's almost experimental," Canter said.

Book of condolences

Members of the public sign a book of condolences at Toronto City Hall for former mayor Rob Ford. (CBC)

Canter said before Rob Ford died that when a patient doesn't respond to chemotherapy, it's important to focus on what time remains.

"It may be better to focus on quality of life, time out of the hospital, time spent with family."

He said additional rounds of chemotherapy may only prolong life by weeks or even days. 

Ford's timeline of treatment

Ford, who was Toronto mayor from 2010 to 2014, began chemotherapy shortly after he was diagnosed with pleomorphic liposarcoma.

In May 2015, he had surgery on the tumour. Last fall, doctors found other tumours on his bladder. Earlier this month, his chief of staff, Dan Jacobs, said Ford had not responded to the latest chemotherapy treatment.

"The toxicity of chemotherapy tends to increase over time," Canter said. "If he's not responding to chemotherapy, that tends to be, unfortunately, a negative sign."

A statement from the Ford family released late Monday said Rob Ford had been receiving palliative care. Doctors had been clear since the diagnosis that he was dealing with an "extremely serious illness" and that he still faced "challenges."

Doctors were "very concerned" about the reappearance and progression of the disease and had been hoping he would get healthy enough for further treatment.

What are the survival rates?

According to the Canadian Cancer Society, survival rates depend on size of the tumour, its type, grade, depth, stage, location and age. Prognosis also depends on treatments chosen and response to treatment

Of the three Canadian physicians with liposarcoma expertise who were contacted by CBC News, none were available for an interview Monday.

Over 8,600 messages

The Ford family set up a get well soon website for Rob Ford earlier this month. As of Tuesday at 2 p.m. ET, more than 8,600 messages had been posted.