Former Toronto mayor Rob Ford is responding to cancer treatment and the tumour in his abdomen has shrunk by 50 per cent, his brother Doug Ford says.

"I am as pleased as punch," the elder Ford brother said Tuesday morning outside Toronto's Mount Sinai Hospital, where Rob Ford is undergoing a fifth round of chemotherapy to treat a rare form of cancer.

"He's doing well. We got a good, positive result. The tumour's reduced by 50 per cent so everyone is happy and positive in the Ford family," Doug Ford said. "It's good news. It's excellent news."

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He added that the treatment is far from over, but the news has raised the spirits of his brother and his family. "It's an emotional rollercoaster," he said. "You still have cancer. It's a long journey, but it's the first piece of positive news we've had in six weeks."

He said the tumour is now about six centimetres wide.

Doug Ford, who stepped into the race for mayor this fall when his brother became ill, said Rob Ford will remain in hospital, receiving chemotherapy until the end of the week. The treatment plan for the former mayor, who is now a city councillor for Etobicoke, includes more tests and 25 days of radiation and possible surgery.

Asked about the performance of the city's new mayor, John Tory, Mr. Ford said he has to "give him a chance."

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He said he has extended an invitation to his former political rival to join him in Florida over the holidays to watch a hockey game. "I've known John for 20, 25 years, I wish him all the best – for the sake of the city, as well," he said.

Ask if his brother will challenge Mr. Tory in four years to his old job, Doug Ford responded, "If he's healthy, he'll run."

The Ford family plans on making a $90,000 donation Wednesday to Humber River Memorial Hospital, with $40,000 coming from the sale of Rob Ford bobblehead dolls and $50,000 coming from the Ford family, Mr. Ford said.