WATCH: Runner surprised by dog battling cancer at Mile 23 of Chicago Marathon

Zissou s cancer is not treatable, but chemotherapy can slow down the progress. He was given an estimated 540 days to live. Sunday s marathon marked day 268. When she began her race, Sampson texted her husband from the starting line For Zissou. Sampson, who also lost her cat to cancer around the same time she learned of her dog s diagnosis, had run nearly the entire race and was just miles from the finish line when she saw her unexpected supporter on the sidelines. Live Like Roo s executive director, Sarah Lauch, joined Sampson s husband, Chris Griffith, in planning the surprise at Mile 23, which was all caught on camera. And for Sampson, the moment was everything. The entire run I thought about all of the times he s gotten up to greet me even though I could tell he was sore and tired, she said. Every single time I come home he is there with a wagging tail. To see him at my lowest when I honestly wanted to quit was everything. It all just really reinforced in me the bond we have with our pets and how important the [Live Like Roo] mission is. In the footage, Sampson is seen crying as she falls to the ground to pet and hug her beloved Zissou, who is wearing a bandana that read happy birthday mom. Zissou in turn offers her a few licks of encouragement. The Live Like Roo Foundation provides support and financial assistance to families whose pet faces a cancer diagnosis. This story uses functionality that may not work in our app. Click here to open the story in your web browser.