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WASHINGTON -- The recent observation of an increasing incidence of colorectal cancer among younger people in the U.S. is also being seen in other developed countries, which has implications for screening recommendations, a researcher reported here.

In the U.S., the annual percent change in colon cancer for individuals age <55 between 1988 and 2007 was +3.08% (95% CI 2.61-3.56), compared with an annual percentage change of -4.20 (95% CI -5.11 to -3.28) for those ages ≥55, according to Rashid Lui, MD, of the Chinese University of Hong Kong.

And for rectal cancer in the U.S., the annual percent change for those <55 was +3.30% (95% CI 2.41-4.20) compared with a change of -3.35% (95% CI -3.82 to -2.87) for those >55, Lui said in a presentation at Digestive Disease Week.

"As we all know, the risk of colorectal cancer increases with age, and the incidence really starts to kick off at around 50 years of age, so most screening programs have recommended starting screening at that time point," Lui said.

A from the American Cancer Society noted that the incidence of colon cancer increased by 1% to 2.4% annually since the mid 1980s in individuals ages 20 to 39, and by 0.5% to 1.3% since the 1990s among those ages 40 to 54, whereas the incidence in those >55 has been declining since the 1980s.

This led the society to issue a just this week that screening begin at age 45 for individuals at average risk. This recommendation also was endorsed by the American Gastroenterological Association.

"These observations also raise the question as to whether the increasing trend among younger adults is limited to the U.S., or whether it is an emerging global problem," Lui said.

Of particular concern is that some studies have suggested that in younger patients, colorectal cancer can present at more advanced stages or even with metastases, he said.

To explore these temporal trends in incidence, Lui's group extracted data from the International Agency for Research on Cancer, analyzing data from six jurisdictions that have collected complete data since 1988: the U.S., the U.K., Sweden, Japan, China (Shanghai and Hong Kong).

From a total population of 113,643,145 individuals, there were 65,909 incident cases of young-onset colorectal cancer as of 2007.

The "young-shift" in colorectal cancer seen in the U.S. was also observed elsewhere. For instance, the annual percent change for rectal cancer in Sweden was +1.26% (95% CI 0.67-1.85) for patients <55 compared with -0.33% (95% CI -0.63 to -0.02) for those >55, and change in colon cancer rates in Hong Kong were +1.65% (95% CI 0.93-2.38) for younger individuals and -1.29 % (95% CI -2.44 to -0.14) for those who were older.

In other areas, there also has been an increase in rates among the younger population without a decline in incidence among older individuals. This pattern was seen for colon cancer in Sweden and Shanghai, and for rectal cancer in the U.K., Hong Kong, and Shanghai.

"This study suggests that earlier colorectal screening should be considered," he concluded, adding that his group plans further work investigating trends in colorectal cancer in developing nations.

Limitations of the study included its cross-sectional design and relative short 20-year follow-up.

Obesity and Colon Cancer

In a separate presentation, Po-Hong Liu, MD, of Massachusetts General Hospital in Boston, explored the potential role of obesity in the "alarming" trends of colorectal cancer in younger patients.

Using data on height, weight, lifestyle, dietary factors, and medications from the Nurses' Health Study II and cancer cases from medical record reviews and the National Death Index, Liu's group identified 121 incident cases of colorectal cancer since 1989 among women age <50, during 1,431,510 person-years of follow-up.

For those whose BMI was ≥30, defined as obese, the multivariate hazard ratio for young-onset colorectal cancer was 1.92 (95% CI 1.08-3.44) compared with those whose BMI was normal. The risk also was consistent among those with a family history of the disease and for those who had not undergone colonoscopy within the previous 10 years.

Further analysis determined that obesity was significantly associated with colon cancer (HR 2.07, 95% CI 1.02-4.20), and nonsignificantly associated with rectal cancer (HR 1.59, 95% CI 0.55-4.60).

Change in weight since adolescence also was associated with an increased risk. Compared with women who had maintained their weight within 5 kg (about 2.2 lbs) since age 18, those who had gained ≥40 kg also had an increase risk of early-onset colorectal cancer (HR 1.96, 95% CI 0.92-4.19).

"Obesity may play a significant role in the pathogenesis of early onset colorectal cancer, through many possible mechanisms such as changes in the microbiota and increases in adipokines," she said.

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