A retrospective cohort analysis of patients from the Surveillance, Epidemiology, and End Results (SEER) program from 1974 through 2013 revealed a surprising increase in incidence of colon and rectal cancers in young adults over the last 20 to 30 years.1

In the late 1970s to mid-1980s, the incidence of colon cancer declined in patients under 50 years of age and increased in patients aged 50 years and older. From the mid-1980s through 2013, however, the reverse was seen: incidence declined in adults over the age of 55 years and increased in the younger population.

The incidence increase (per year) was 2.4% for adults aged 20 to 29 years and 1.0% for adults aged 30 to 39 years. In the mid-1990s, rates also increased for adults aged 40 to 49 years (1.3% per year) and 50 to 54 years (0.5% per year).

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But in adults 55 years and above, the rates declined over the entire study period.

Compared with adults born in around 1950, those born around 1990 are at a 2-fold higher risk for colon cancers and a 4-fold higher risk for rectal cancers.

“The age-specific risk for people born around 1990 is almost the same as for those born around 1890,” Rebecca L. Siegel, MPH, an epidemiologist at the American Cancer Society in Atlanta, Georgia, and lead author of the paper, told Cancer Therapy Advisor. “The increase in rectal cancer rates is of a much larger magnitude and goes on for a longer time,” she said.

Alan Venook, MD, a colorectal cancer specialist who was not associated with this study, qualified these observations. “These are relative incidence rates and are still not common events,” he said. “The observation that the distribution is moving to younger patients is unusual.”

He explained that the report may also have an ascertainment bias. “Are you biasing the observation because you are looking for it more often?” he asked and indicated that the analysis may be “nuanced biostatistics.”

Dr Venook is The Madden Family Distinguished Professor of medical oncology and translational research and is associate director of program development at the Helen Diller Family Comprehensive Cancer Center, University of California at San Francisco.

Dr Venook indicated, however, that he is not surprised with this report.

“We know that surveillance decreases the risk of colon and rectal cancer by eliminating polyps and so the incidence of the cancer is decreasing. Since we generally recommend surveillance when patients turn 50, we would expect that fewer patients in their 60s and 70s would be getting colorectal cancer,” he said.

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“So, statistically, a greater percentage of cancers would now occur in younger patients,” he added. If the absolute number of cases of cancer in younger patients is increasing, then this raises the question of causes and whether clinicians should be screening even younger patients.