PEOPLE TREATED FOR early-onset colorectal cancer are at an increased risk of being diagnosed with a subsequent cancer, according to a preliminary study presented at Digestive Disease Week in May 2023. The study results are noteworthy given the growing prevalence of early-onset colorectal cancer in the U.S. and Europe. Early-onset disease is a cancer diagnosed before age 50.

“Colorectal cancer is the third leading cancer diagnosed in the United States, with approximately 153,000 people estimated to be diagnosed with it in 2023,” says Aniruddha Rathod, a postdoctoral researcher at the UT Southwestern Medical Center in Dallas, the study’s lead researcher. Roughly 11% to 12% of people diagnosed will be under age 50.

Using cancer registry population data from the National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) Program, the study looked at 7,041 survivors ages 18 to 49 diagnosed with stage 0 to III colorectal cancer between 1992 and 1999. Rathod and his team found that 16% of people in the data set—1 in 6 of those treated for early-onset colorectal cancer—went on to be diagnosed with a subsequent cancer. The four most common types of secondary cancer diagnosed were colorectal, prostate, breast and lung. Although approximately one-third of the 1,131 cancers diagnosed after treatment were colorectal, “most of these secondary cancers were not colorectal cancer,” Rathod says. In the study, the risk of a secondary cancer among early-onset colorectal cancer survivors was slightly higher in men versus women.

A secondary cancer is not the same as a cancer recurrence. “It’s a completely new cancer, with a different pathophysiology and subtype than the previous cancer,” says Hyuna Sung, senior principal scientist and cancer epidemiologist at the American Cancer Society Surveillance and Health Equity and Science Department. Dr. Sung was not involved in the study.

With the population of people who have survived colorectal cancer growing rapidly, expanded guidelines are being developed by professional organizations, such as the American Society of Colon & Rectal Surgeons and the American Cancer Society for monitoring early-onset colorectal cancer survivors to detect future colorectal cancer. “But there are no specific guidelines available for screening people who have had early-onset colorectal cancer for other types of cancer, such as prostate, breast or lung cancer,” Rathod says.

In general, cancer survivors have a 10% higher risk of being diagnosed with a subsequent cancer, compared with the overall population, with lung cancer the most common secondary cancer diagnosis, Sung says. The secondary cancer may develop 10 or 15 years after the original diagnosis. Exposure to cancer treatment that has been associated with heightened cancer risk is the strongest predictor of the risk of a second cancer, she says. Patients who undergo breast cancer treatment, for example, may be at increased risk for lung cancer later on due to radiation exposure to the chest, and they may be advised to undergo regular lung screening after they finish treatment.

Similarly, research shows that early-onset colorectal cancer treatment may heighten the chance of getting cancer again due to the use of specific types of chemotherapy or high doses of radiation. The increased risk of a secondary cancer after early-onset colorectal cancer may also be due to other factors, such as a genetic mutation related to cancer formation, Rathod says.

“Given what we showed in our study with early-onset colorectal cancer, there is an opportunity to refine the screening and surveillance strategies for people diagnosed with early-onset colorectal cancer for other types of cancer,” Rathod says. Due to National Cancer Institute (NCI) criteria, however, patients with a history of cancer treatment are typically excluded from participating in clinical trials that could help refine these strategies. “We need to do additional studies to inform comprehensive, evidence-based screening and surveillance recommendations for this growing population of early-onset colorectal cancer survivors and the risk of subsequent cancers,” Rathod says.

In the meantime, if you are diagnosed with early-onset colorectal cancer or have a prior history of any cancer, “mention your cancer diagnosis to your primary care physician, who may be able to guide you about any prevention guidelines in place,” Sung says. Screening guidelines are constantly evolving as science advances. In addition to seeing your oncologist and primary care doctor for follow-up and preventive care, Sung recommends doubling down on reducing your risk of a second cancer by following NCI guidelines for lowering the risk of cancer in general: exercising regularly, eating a healthy diet, avoiding or limiting alcohol, maintaining a healthy weight, and quitting smoking.

Sandra Gordon is a medical writer in Stamford, Connecticut.