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Dave Canon, a Chicago Heights native, is running his first marathon to fulfill a promise he once made to himself when "I was as down as you could get." 

Canon was undergoing radiation treatment for testicular cancer, 80 pounds overweight and at a low point. 

His college roommate, Mike Daley, always encouraged him to run. Radiation treatment led Canon to finally make the promise to run.

"I was going to make a comeback," Canon said. 

In the last 18 months, Canon has lost 80 pounds. Changing his diet and training has helped him change his lifestyle.

In the beginning of his training, Canon said he ran a 13:30 minute mile. Now, after completing his first half-marathon, his pace has increased to a 9:16 minute mile.

"The marathon is a metaphor for my life right now," he said. "You have to keep moving forward, there will be pain, you will suffer. You will have days you feel lousy and days you feel great, but you have to put in the miles nonetheless."

The 40th anniversary of the Bank of America Chicago Marathon steps off Oct. 8, 2017. Here's how you can watch it live on TV and online.