When Kayla Bradford was pregnant with her first son, she developed an unshakeable cough.

Her doctor chalked it up to swelling and acid reflux, and Bradford figured it would clear up after she gave birth. It didn't.

Doctors eventually ordered an X-ray, which revealed the devastating news: Bradford had lung cancer, and the disease had spread to her brain, bones and liver.

The diagnosis came as a shock to the 25-year-old, who has never picked up a cigarette.

"There wasn't an explanation why -- just anyone with lungs can get lung cancer. It doesn't have to be from smoking necessarily, and unfortunately I was one of the unlucky ones," Bradford told CTV News.

She instantly went into "fight mode" against the disease. But when it came to breaking the news to others, Bradford felt pushed on the defensive.

"I feel I always need to assure them I never smoked, because I just assume that the first thing they are going to think is I did it to myself from smoking," Bradford told CTV News.

No cancer is deadlier than lung cancer. The Canadian Cancer Society estimates that, in 2017, 28,600 Canadians will be diagnosed with the disease, and 21,200 will die. That's more fatalities than colon, breast and prostate cancer combined.

While smoking is the number one cause of lung-related cancers, non-smokers like Bradford are increasingly being diagnosed. About 15 per cent of patients with lung cancer have never smoked, according to Lung Cancer Canada. That amounts to some 5,600 non-smokers in Canada diagnosed with lung cancer each year.

Those rates appear to be rising. A U.S. study published last year found that the rate of non-smokers with lung cancers increased from 8 per cent in the early 1990s to 14.9 per cent between 2011 and 2013. The increase was seen across age, sex and ethnicity, leading researchers to conclude that the actual incidence in lung cancer among non-smokers has jumped.

In Canada, doctors have noticed a similar trend. Dr. Rosalyn Juergens, chair of the Lung Cancer Disease Site Team at the Juravinski Cancer Centre in Hamilton, Ont., regularly sees non-smokers with lung cancer in her office.

"I have 20-year-olds, 30-year-olds. I have booked a patient who is 40 with an infant. This is every day for me," said Jurgens, who estimates that up to 20 per cent of Canadians with lung cancer have never smoked.

Scientists don't know why those rates appear to be rising. Several studies are underway, and factors such as radon gas, air pollution and certain chemicals found at home and work are under analysis.

As researchers hunt for an answer, the medical community is raising awareness about the stigma facing non-smokers with lung cancer.

A survey released last week by the Global Lung Cancer Coalition found that 20 per cent of Canadians admit they have less sympathy for a person with lung cancer than other forms of the disease.

That's slightly less than in the U.S., where 27 per cent of Americans surveyed said they had less sympathy.

Overall, compassion for lung cancer appears to have dwindled. In 2017, 53 per cent of Canadians surveyed said they thought lung cancer patients deserved sympathy, down from 61 per cent in 2010.

Canadians who've never smoked should not be quick to dismiss the possibility of lung cancer, and neither should their doctors, Jurgens said.

"When you have a young never smoker with a cough, you are thinking acid reflux, asthma. If you have a cough that doesn't go away, push for a chest X-ray so we can get a good idea of what is going on," she said.

Besides smoking, Jurgens points to a variety of factors linked to lung cancer.

Radon gas, which occurs naturally in nature but can become dangerous when concentrated in homes, accounts for more than 21,000 lung cancer deaths in the U.S. each year, according to the U.S. Environmental Protection Agency. Exposure to the substance is the leading cause of lung cancer in non-smokers.

Second-hand smoke, air pollution, regular exposure to carcinogens like asbestos and diesel fumes, and gene mutation may also play a role, Jurgens said.

Bradford underwent chemotherapy and radiation and is now stable. She also had a biomarker test, which determined her type of cancer -- ALK+ -- and pinpointed the best treatment possible. She is now on new immunotherapy medications that boost the body's immune defences to fight cancer.

Bradford said she now feels well, with few side-effects.

She's also started a support group, Kayla's Fight Club, to raise awareness and money in the event that she needs to undergo new experimental treatments.

For her, the single greatest motivator is her newborn son, Leighton, now a healthy 1 year old.

"I want to watch my son grow up, so that gives me the motivation to fight every single day," she said.

With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip