Cancer rates in people younger than 50 are rising, new study finds. Doctors don't yet know why.

Rates of colorectal cancer have been increasing in young people over the past few years — and have gotten a lot of attention in the process. But disturbing new research finds that rising cancer rates in young people aren't limited to colorectal cancer.

The study findings, which were published in JAMA Network Open, "build on data that's been previously presented and observations that have gotten public interest," Dr. Jack Jacoub, a medical oncologist and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in Fountain Valley, Calif., tells Yahoo Life. "It's very, very powerful information."

Which forms of cancer are increasing in young people and, more importantly, why is this happening? Doctors break it down.

What the study says

The new study finds that early-onset cancer — defined as cancer in people younger than age 50 — increased from 2010 to 2019.

What are the key findings?

This study analyzed data from 17 National Cancer Institute Surveillance, Epidemiology and End Results registries from Jan. 1, 2010, to Dec. 31, 2019, and included 562,145 patients who were diagnosed with early-onset cancer.

During that time, the researchers found that rates of early-onset cancers increased overall and in females. However, rates of such cancers decreased in males.

In 2019, the highest number of cases of early-onset cancer were in the breast — 12,649 — but during the study period, gastrointestinal cancers had the fastest-growing rates of early-onset cancer. Among gastrointestinal cancers, those with the fastest-growing incidence rates were in the appendix, followed by cancers of the bile duct and pancreas.

This research "may be useful for the development of surveillance strategies and funding priorities," the researchers wrote.

What experts think

Doctors say the findings are important. "We are well aware that there is an increase in colorectal cancer in younger people under age 50, but we weren't aware that the cancers that are growing more rapidly are more unusual cancers like appendix cancer and biliary cancers," Dr. Anton Bilchik, a surgical oncologist and chief of medicine at Saint John’s Cancer Institute in Santa Monica, Calif., tells Yahoo Life.

As for why this is happening, that's still being explored, Dr. Christopher G. Cann, assistant professor at Fox Chase Cancer Center in Philadelphia, tells Yahoo Life. "The oncology research community still does not have a firm understanding of the underlying cause of this rise in early-onset cases," he says. "Current research suggests early-onset gastrointestinal cancers may be influenced by changes in bacterial species of gut microbiome, early antibiotic exposure or environmental carcinogens."

The obesity epidemic may also be associated with this, Jacoub says. "Everyone has recognized that the American population is more obese than other populations in the world," he says. "There are a lot of downstream issues from obesity — hormonal changes and inflammation — that may lead to an increased incidence of cancer."

Another factor may be that younger people are being screened for cancer more than they were in the past, Bilchik says. "We're doing a better job at screening," he says, noting that breast cancer is probably one of the cancers most often screened for in people under 50. "We've also reduced the age of screening for colorectal cancer to age 45," Bilchik points out.

"Perhaps there is also more awareness that cancers don't always occur in older people," he says. "But there are other factors involved that we can't quite explain."

Why it matters

Cann says it's important for younger people and the medical community to pay attention to the findings. "It is imperative that we increase awareness of this alarming trend to the public and encourage young adults to reach out to their medical provider if concerns ever arise," he says.

Jacoub says it's also crucial for medical providers not to assume their younger patients can't have cancer. "Providers shouldn't simply look for other reasons for symptoms because they think, 'Who is going to get cancer at 35?'" he says. "We need to include it in the list of possibilities for health issues."

He calls the study findings "enlightening" and an "important observation."

"Health care providers will be paying very close attention to this," he says. "This will be what is taught to future doctors."