Doug Ford says the tumour — which doctors had initially said was 12 centimetres in size — is now down to six centimetres.
He says his brother will be finishing the fifth round of chemotherapy in a few days.
After that, he says the former mayor will be getting radiation treatment, although he was not sure of the schedule.
Ford was diagnosed with a rare and aggressive form of abdominal cancer back in September and dropped his bid for mayoral re-election shortly afterwards.
Instead, he ran for a seat on city council and was voted in during the Oct. 27 municipal election.
At a news conference at Toronto's Mount Sinai Hospital in September, Dr. Zane Cohen said Ford had been diagnosed with a type of cancer that arises from fat cells and can attack a variety of soft tissues in the body.
He described the tumour at that time as 12 centimetres by 12 centimetres in size.
During an appearance at city hall in late November, Rob Ford said that his tumour hadn't shrunk, but it hadn't gotten larger either.
While the family is happy to now be getting more positive news, Doug Ford said his brother still has a long journey ahead of him, calling it an "emotional roller-coaster."
"He's doing well," Doug Ford said, adding: "I'm all smiles."
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