The report is published in the Nov. 10 online edition and the Dec. 1 print issue of the Journal of the National Cancer Institute.
Shahinian and colleagues used data from the Surveillance, Epidemiology, and End Results database of the U.S. National Cancer Institute.
The researchers identified 107,859 men aged 67 years or older diagnosed with prostate cancer between 1993 and 2002, and followed-up through 2004.
The investigators found a 30 to 40 percent relative increase in the rate of colorectal cancer among the men who received hormone therapy compared with those who did not.
The longer the men received hormone therapy, the greater was their risk of developing colorectal cancer, the researchers found. The highest risk was seen in men who had their testicles removed.
Jennifer H. Lin, an instructor in preventive medicine at Brigham and Women's Hospital in Boston and co-author of an accompanying journal editorial, said this is the first large observational study showing that androgens may prevent colorectal cancer development in men.
Earlier research has shown that hormone replacement therapy lowers the risk for colorectal cancer in postmenopausal women, she added.
"Obesity is an important risk factor, especially in men, for colorectal cancer development," she added. "Obese men also tend to have lower androgen levels, suggesting a potential role of androgens in colorectal cancer development."
The findings support the need for routine screening for colorectal cancer and the adoption of lifestyle practices, such as physical activity, to help prevent colorectal cancer, she said. "This is especially important among prostate cancer patients who undergo anti-androgen therapies," Lin stressed.
Dr. Anthony D'Amico, a prostate cancer expert at Brigham and Women's Hospital, sees the study results differently.
"This is a classic example of true, true and unrelated," he said. Many me
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