Canadian doctors have observed a “rapid increase” in the number of patients under age 50 with colorectal cancers and they can’t explain why.

A new study, led by doctors from the University of Toronto, looked at Canadian Cancer Registry data from 1997 to 2010 and found that incidences of colorectal cancer rose by:

0.8 per cent per year for people in their 40s,

2.4 per cent per year for people in their 30s, and

6.7 per cent per year for those between ages 15 and 29.

The growing rates in young people come after decades of declining rates in people over 50, which have occurred “most likely due to increased use of colorectal cancer screening which can identify and remove precancerous polyps,” according to the Canadian Cancer Society.

The study, published online in Cancer Epidemiology, mirrors findings reported in Europe, Australia and the United States.

One of those U.S. studies, led by Dr. Elie Sutton of Mount Sinai Hospital in New York, looked at a million people. It found an 11.4 per cent increase over 10 years in new cases among those under 50 -- an annual increase of 1.28 per cent.

That was compared to a 2.5-per-cent decrease over 10 years for those 50 and over.

Dr. Sutton said his study confirmed what doctors are seeing in their practices. The study also found that young people are getting diagnoses at later stages, when they are harder to treat.

“These are cases of potentially treatable colorectal cancer that we’re not catching early enough,” he said.

Causes not clear

Risk factors for colon cancer include being male, eating processed meats and red meats, a lack of dietary fibre, a lack of physical exercise, obesity, alcohol, smoking, diabetes and genetics, according to the Canadian Cancer Society.

But Prithwish De, director of the Ontario Cancer Surveillance Program and co-author of the new study, said more research is needed to explain what’s causing the “rapid increase” among younger people.

De said the fact that incidence is rising only among younger people suggests “lifestyle” factors are at play, but he isn’t sure which ones.

The study noted that weight had risen “substantially” in the people it reviewed, physical activity had declined somewhat, alcohol consumption was little changed and smoking rates had gone down. Data on dietary choices were not available.

Shock and disbelief

Despite living a healthy lifestyle, Discovery Channel Producer Denise Kimmel was diagnosed with colon cancer in her 40s and spent the last year undergoing surgeries, radiation and chemotherapy.

“It was a lot of shock and even more disbelief,” she said. “Because traditionally you are told to get screened when you’re over 50.”

Kimmel said her doctors “weren’t shocked,” however, noting that they had diagnosed a few younger people, including a 30-year-old vegan yoga instructor.

Paul Greenberg, from Colon Cancer Canada, also had no risk factors when he was diagnosed in 2000 at age 39.

The symptoms that sent him to the doctor’s office were “subtle,” and included fatigue, facial bloating and a small amount of rectal bleeding, he said. His doctor performed surgery immediately.

“At 39 you still have a really big head about nothing being able to hurt you and all of sudden you are knocked to the ground,” Greenberg said. “I had just gotten engaged to my now wife and we were looking at a life ahead and then this thing hits us.”

“What scares me most about it is that no one can tell anyone else what they can do to avoid this,” he said.

Should screening guidelines change?

It is currently recommended that all Canadians between the ages of 50 to 74 years old have a stool test every two years to look for blood that may indicate colorectal cancer. If blood is found, a test like a colonoscopy may be ordered.

Greenberg said he isn’t sure whether the new study means all people under 50 should be screened, but he thinks people of all ages should see a doctor if they have symptoms, which can range from blood in stool to a decrease of appetite to weight loss.

Kimmel said she thinks earlier screening -- perhaps at age 40 -- would help. “The earlier you can get screened, the earlier you can get treatment, the greater your chances of survival,” she said.

De said that while it’s true that earlier treatment improves changes of survival, there isn’t yet enough evidence yet to change screening guidelines. There are some reports that US officials are currently looking at revising screening guidelines.

“It really up to individuals and their health care providers,” he said, “…to catch that early enough so treatment can be given.”

Dr. Shady Ashamalla, a surgical oncologist at Sunnybrook Health Sciences in Toronto, agrees that doctors need to be more vigilant. “We are not used to thinking ‘this is colon cancer in this 25-year-old with bleeding in their stool,’” he said.

About 25,000 people are diagnosed with colorectal cancer each year in Canada. About 9,300 die.

Two-thirds of patients are still alive five years after diagnosis, according to the Canadian Cancer Society.

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