By Dr. Mallika Marshall

BOSTON (CBS) – Chicago firefighter Jim O’Malley’s cancer was caught by a group of dogs. “At first I didn’t believe it at all,” he said.

Since 2013, O’Malley and hundreds of his fellow Chicago firefighters have breathed into masks as part of a study. The breath samples are tested by dogs trained to sniff out cancer. A raised paw means a sample is positive.

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“I thought this is crazy,” he said. At 49, O’Malley didn’t believe what the dogs had discovered. Then he went to his doctor. “They said you have colon cancer. And it really took the wind out of my sails. I was like ‘whoa.'”

Within a month O’Malley had lifesaving surgery. “A lot of people shake their head and say ‘no way.’ No way a dog can figure this out.”

But it turns out dogs may be figuring it out. Out of 700 Chicago firefighters screened in 2016, 18 were accurately identified as having cancer and four tested positive for pre-cancer.

Breath samples tested by dog trained to sniff out cancer (Image from

Breath samples tested by dog trained to sniff out cancer (Image from

“I think the dogs are detecting a cocktail of odors,” explained Glenn Ferguson, founder of Cancer Dogs. He says the dogs are catching cancer 95% of the time and often before traditional screenings.

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“Almost every guy that I came out with is dead from cancer. And you see them go. It’s terrible,” said chief steward Mike Butkus.

He says the dog test was a tough sell at first at his Chicago fire house.

“I’ve had guys call me saying you shouldn’t be offering this because it’s nothing but voodoo,” Butkus said.

But don’t tell that to the O’Malleys.

“They saved my husband’s life, absolutely. No doubt,” said Jim’s wife, Liz. Jim agrees, “I truly believe that if I had not done the breath screening there’s a chance I might not be here.”

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The breath test is not yet available to the public. There is a new lab for cancer sniffing dogs opening in the U.S. in March and they hope to recruit more firefighters from around the country, including from here in New England, to try out the test. We’ll keep you posted.

Dr. Mallika Marshall