The hardest part of battling a rare and aggressive form of cancer has been explaining it to his school-age children, Toronto Mayor Rob Ford said Thursday, admitting he sometimes cries himself to sleep.

"The kids, it's ripping my heart out," a pale and tired-looking Ford told reporters outside his city hall office.

"Some nights I just cry myself to sleep, but what can you do, there's only that many tears that can be shed," he said hoarsely.

Ford began chemotherapy last month after doctors found a tumour in his abdomen, with another round of the treatment scheduled to start next week.

The mayor said doctors have told him there's a 50/50 survival rate for his condition but stressed he always "sees the glass as half full" and is taking it "day to day."

The diagnosis prompted Ford to pull out of the mayoral race to run for city council instead. His councillor brother Doug is now gunning for the mayor's seat.

Ford said it's hard to predict whether he'll be able to take part in any debates ahead of the Oct. 27 election because his energy levels vary so much.

Earlier in the day, he said chemotherapy has "knocked the you-know-what" out of him but he remains optimistic.

He also said fighting cancer has been his biggest challenge in a year plagued with scandal, including his admitted drug use and a stint in rehab for alcohol abuse.

"A lot of the stuff that I've gone through most of it's been self-inflicted but when you get hit with cancer, that's not self-inflicted. This is by far the worst event, it's taken its toll on me," he said.

"I saw it with my dad, but I didn't feel it, I wasn't in his shoes, but I saw what he went through. And I just told the doctors, I just don't want to suffer."

Ford's father — Doug Ford Sr. — died of colon cancer in 2006.