For the first time, colorectal cancer is the top cause of cancer deaths among people younger than 50 in the U.S., according to a new study from the American Cancer Society.

Researchers relied on National Cancer Institute data from nearly 1.3 million people in this age group who died of cancer between 1990 and 2023. The sharp rise in early-onset colorectal cancer clouds an otherwise encouraging result: overall cancer deaths are down 44%.

The other four leading killers — brain, breast and lung cancer as well as leukemia — have declined in mortality. Lung cancer deaths have fallen especially quickly, declining almost 6% year-over-year between 2014 and 2023.

Breast cancer held the top spot for about a decade prior to 2023. It remains far and away the leading cause of cancer deaths among younger women, however, at least doubling colorectal cancer mortality.

Scientists have been aware of climbing colorectal cancer rates among people in their 20s, 30s and 40s for years, but have yet to pinpoint the primary cause — if one exists at all.

Risk factors for developing the disease early may include poor diet, sedentary lifestyle, certain genetic variations and disruptions to the gut microbiome, according to the Mayo Clinic.

“While we await answers for why colorectal cancer rates are up, lives can be saved now through symptom awareness and destigmatization, and more screening uptake, as three in four people under 50 are diagnosed with advanced disease,” said Rebecca Siegel, senior scientific director of surveillance research at the American Cancer Society and the study’s lead author.

The group recommends people at average risk of colorectal cancer receive regular screenings starting at age 45. Those at high risk may need to start sooner.

Symptoms of colorectal cancer include changes in bowel habits lasting more than a few days, rectal bleeding, a persistent feeling of fullness, abdominal pain, fatigue and unintended weight loss, according to the American Cancer Society.

A majority of colorectal cancer diagnoses still occur in people 50 and older.

An analysis from the American Cancer Society released earlier this month found a record 70% of cancer patients are living five years past their diagnosis, up from just 49% in the mid-1970s.