Former Toronto mayor Rob Ford's tumour appears to be shrinking, his brother Doug Ford confirmed on Tuesday morning.

The update comes as Rob Ford, who was diagnosed with pleomorphic liposarcoma in September, prepares for a fifth round of chemotherapy at Toronto's Mount Sinai Hospital.

In October, Rob Ford told media that the tumour did not appear to be shrinking, but after two more rounds of chemo it appears that the treatment is working.

"He's doing well," Doug Ford told reporters outside the hospital on Tuesday.

"He's positive today. He was really upbeat, it was great."

When the former mayor’s diagnosis was made public, his doctor said the abdominal tumour measured 12 centimetres by 12 centimetres. Now, Doug Ford says it has shrunk to approximately half that size.

"I'm all smiles. I just want to thank the people at the hospital - the doctors, the staff and everyone," Doug Ford said, thanking supporters, and "even people who may not agree, politically" for their kind words.

"There's still a long way to go and we're praying every day...It's a long haul. It's not over yet," he added, explaining that, depending on the results of the chemotherapy, Rob Ford may still need to undergo radiation treatment.

Following his diagnosis, Rob Ford dropped his bid to be re-elected as mayor. Instead, he ran in Ward 2 (Etobicoke North) and was elected as city councillor in October.