SYRACUSE, NEW YORK — Rectal cancer deaths among adults ages 20 to 44 have risen up to three times faster than colon cancer deaths since 1999 and could surpass colon cancer mortality by 2035, according to preliminary research from SUNY Upstate Medical University in Syracuse, New York. The study, which has not yet been peer-reviewed, is scheduled to be presented at a national meeting of gastroenterologists in May.

Researchers analyzed Centers for Disease Control and Prevention death records from 1999 through 2023 for people ages 20 to 44. Deaths from early-onset colorectal cancer overall rose during that period, with the rate of rectal cancer deaths accelerating the most. Hispanic adults saw the steepest rise in rectal cancer deaths and had the fastest-growing mortality rates of any demographic group.

"The rate of rectal cancer seems to be increasing more than two to three times compared to colon cancer," said Mythili Menon Pathiyil, lead author of the study and a gastroenterology fellow at SUNY Upstate Medical University. The researchers did not identify why the tumors were increasing or whether they are becoming more aggressive.

Colon cancer is currently the nation's leading cause of cancer death in people under age 50, and colorectal cancer rates have been increasing 3% each year for adults under age 50 since the late 1990s. The findings build on an American Cancer Society study released in March showing that a rise in rectal cancer rates is driving increases in colorectal cancer diagnoses in people younger than 65. The American Cancer Society projects 158,850 new colorectal cancers will be diagnosed in 2026 and about 55,230 patients will die from the disease that year, with nearly a third of those deaths in people under age 65.

"This is a medical crisis," said Ben Schlechter, a gastrointestinal medical oncologist at Dana-Farber Cancer Institute in Boston. He said the cause likely predates the affected generations. "It seems the bulk of such cancers leading the surge in cases today are not hereditary. An exposure to increase the risk likely occurred in the 1960s or 1970s," Schlechter said.

Colon cancer and rectal cancer form in different parts of the digestive tract. Standard treatments for rectal cancer include surgery, radiation, and chemotherapy to the pelvic region, which might affect a patient's bladder, bowel and sexual functioning. Scientists are working to find common links among younger adults who develop rectal cancer as they reach their 30s and 40s. "If we could 'Magic School Bus' our way into the tumor, we could see what's going on inside those cells," said Andreana Holowatyj, an assistant professor of hematology and oncology at Vanderbilt University Medical Center.