Incidence of Rectal Cancer Increasing in Adults Younger Than 40 Years

Kathleen Louden

August 26, 2010

August 26, 2010 — The incidence of cancer of the rectum and rectosigmoid junction increased nearly 4% annually between 1984 and 2005 in Americans younger than 40 years, reports a study published online August 23 and appearing in the September 15 print issue of Cancer.

"The incidence of rectal cancer in the United States in young patients is considered to be low. Underestimating this incidence may result in a failure to diagnose younger patients with rectal cancer in a timely manner," write Joshua Meyer, MD, from New York–Presbyterian Hospital/Weill Cornell Medical Center in New York City, and colleagues.

After observing an increase in rectal cancer in patients at their institution who were younger than 40 years, the investigators analyzed nationwide trends in rectal cancer incidence using the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) cancer registry database.

Using SEER data from between 1973 and 2005, the researchers identified the number of patients younger than 40 years who had a diagnosis of cancer of the rectum, rectosigmoid junction (rectosigmoid), or colon. The researchers also estimated the annual percentage change for each anatomic site, using the weighted least squares method, and calculated the 95% confidence interval (CI).

Of the 7661 young patients with colorectal cancer, the greatest percentage — 67% — had colon cancer (n = 5125); 25%, or 1922 patients, had rectal cancer; and 8% (614 patients) had rectosigmoid cancer. During the years of the study, the incidence per 100,000 was 1.11 for colon cancer (95% CI, 1.08 - 1.14), 0.42 for rectal cancer (95% CI, 0.40 - 0.44), and 0.13 for rectosigmoid cancer (95% CI, 0.12 - 0.14).

In an age breakdown, 52% of the patients were 35 to 39 years old, 28% were 30 to 34 years old, and 20% were younger than 30 years.

Colon cancer had no statistically significant annual change. Only rectal cancer and rectosigmoid cancer increased in incidence over time, the authors found. The annual percentage change for rectal cancer was 2.6% (95% CI, 1.9% - 3.3%), and for rectosigmoid cancer it was 2.2% (95% CI, 1.2% - 3.1%; both P < .0001).

The investigators pooled these 2 groups for trend analysis, using joinpoint regression modeling software, to find the year that the incidence began increasing. They found a single joinpoint at 1984. Between 1984 and 2005, the annual percentage change for rectal and rectosigmoid cancer combined was 3.8% (95% CI, 2.8% - 4.8%).

"All races and both sexes demonstrated similar statistically significant increases in the incidence of rectal and rectosigmoid cancer," Dr. Meyer and colleagues write.

Reasons for the rising incidence in these cancers among younger patients are unclear. After reviewing the literature looking for explanations, including changes in screening techniques and lifestyle risk factors, the authors could find no reason that would also account for the lack of an increase observed in colon cancer during the study period.

Among the limitations of the SEER database, according to the authors, are that it does not capture family history or a diagnosis of familial adenomatous polyposis or hereditary nonpolyposis colorectal cancer, and that it contains no standardized definition of rectum or rectosigmoid sites. In addition, the geographic regions that participate in the registry have greatly expanded in the last decade, which the authors report complicates the longitudinal analysis.

Still, the findings have clinical importance, according to the authors, because individuals younger than 40 years tend to not be screened for colorectal cancer unless they are at high risk. Furthermore, rectal bleeding, the most common presenting symptom of colorectal cancer, often is mistakenly attributed to hemorrhoids in younger patients, studies show.

Although the authors do not recommend changing current screening guidelines for colorectal cancer, they suggest endoscopic evaluation of young patients who have rectal bleeding or other common signs and symptoms of rectal cancer.

They conclude: "Although colonoscopy may not be warranted, we suggest that flexible sigmoidoscopy, at a minimum, should be performed in this setting to rule out rectal or rectosigmoid cancer."

Study coauthor Paul Christos, DrPH, reported that he received partial funding from the Clinical and Translational Science Center at Weill Cornell Medical College, New York City. The other authors have disclosed no relevant financial interests.

Cancer. 2010;116:4354-4359. Published online August 23, 2010.

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