CHICAGO (CBS) — An alarming trend has doctors concerned.

Colo-rectal cancer rates have declined for years, but now health experts have seen a spike in rates among young people in their 20s and 30s.

READ MORE: Family Sues After They Say Chicago Police Burst Into Their Home, Pointed Guns at Kids in 2019

As CBS 2’s Dr. Max Gomez explained, colo-rectal cancer is the second leading cause of cancer deaths in the country behind lung cancer.

Each pregnancy for Chaya Biskin-Sitko seemed to get harder and more painful, but it took years for her doctors to figure out why.

“I’ve never even considered colon cancer as a thing. I thought old men get that,” she said.

The 33-year-old mother of three is one of a growing number of young people diagnosed with colo-rectal cancer, according to a new American Cancer Society study.

It shows people born in 1990 have twice the risk of colon cancer and four times the risk of rectal cancer as people born in 1950 faced at the same age, but the question is why?

“That’s the million dollar question, we don’t know,” Dr. Andrea Cercek said.

READ MORE: Woman Pistol-Whipped On CTA Blue Line Train In Bucktown

Dr. Cercek of Memorial Sloan Kettering Cancer Center said the increase is not linked to family history, so environmental factors are likely to blame.

“Some of it may be due to the fact that there have been changes in young people, in the millennial generation, in terms of a more sedentary lifestyle, dietary changes, obesity may play a role but that is not really clear,” Dr. Cercek said.

Current guidelines recommend screening at age 50 for people at average risk, making it hard to catch in younger patients.

“Although the date do not completely support early screening we may want to consider it,” she said.

Chaya had surgery and chemotherapy to treat her stage four cancer.

“If you have any symptoms, if you’re bleeding at all, if your stomach is hurting, if something is not going right, if you’re not feeling 100 percent, don’t just go to one doctor and take their word for it,” she said.

She hopes her story will bring awareness to a group that may think this can’t happen to them.

MORE NEWS: Woman Injured In Crash On DuSable Lake Shore Drive, Good Samaritans Help Her Escape Burning Car

Experts stressed that the absolute number of colo-rectal cancer in young people is still very low. Americans over age 50 are actually 16 times more likely to get that cancer. Doctors say a a high-fiber, low-fat diet can reduce the risk of developing colorectal cancer.