With biopsy results expected by the end of the week, Ford's illness raised the possibility that he might have to pull out of the October 27 election after having clung to power through a string of scandals, including his appearance in expletive-ridden videos and accusations that he ordered a jailhouse beating.
Ford's brother and campaign manager, Doug Ford, was expected to update the city on the mayor's health and political future on Thursday, but pundits were already mulling the mayor's options in a close-run election race in which Ford is one of three frontrunners.
"To some extent or another, the future of the city rests in the status of a tumor in the mayor's belly," columnist Edward Keenan wrote in the Toronto Star, the city's biggest daily newspaper and the one most critical of Ford.
"Whether he can carry on and fight, and what that will mean for his support, whether he needs to withdraw and turn a campaign that has been largely about his governance on its head, whether his brother might run in his place. The decisions need to be made soon," Keenan wrote.
Friday is the deadline for candidates to remove their names to the ballot and for new ones to be added. Rob Ford's brother Doug is also a city councillor.
News of the tumor broke in the early evening on Wednesday after the mayor went to hospital complaining of unbearable abdominal pains.
"It's not a small tumor," the hospital's president said, noting that Ford had been suffering from pain for more than three months.
Rob Ford's father, Doug Ford Sr., a politician and businessman, died of colon cancer less than three months after being diagnosed in 2006.
In 2009, doctors removed a tumor from Rob Ford's appendix but the then-city councillor returned to work in good health.
The mayor spent two months in rehab for drug and alcohol abuse in May and June, emerging noticeably thinner though still obese. He said he regretted not getting treatment "years ago" to treat his alcohol addiction.
Ford, who came to power in 2010 pledging to cut waste at city hall and keep a lid on taxes, has a core base of suburban support, but he has come under fire for use of crack cocaine and for several videos showing him drunk, spewing racial slurs, and threatening violence.
His two main opponents in election wished the mayor well as they went ahead with a two-hour breakfast debate on Thursday that Ford had been scheduled to attend.
A poll released on Wednesday showed Ford running in second place with 28 percent of the vote, behind conservative frontrunner John Tory, who had 40 percent of voter support. Left-leaning candidate Olivia Chow was in third place with 21 percent of the vote.
