The total number of Americans dying from or diagnosed with cancer is falling, but certain cancers linked to obesity and inactivity are on the rise, according to an annual report on the status of cancer in the United States.
U.S. cancer rates fell 0.6 percent per year between 2004 and 2008, according to the report, based on data from the National Cancer Institute, the Centers for Disease Control and Prevention and other sources.
For men, the incidence of prostate cancer dropped by an average 2.1 percent per year, while lung cancer rates fell 2 percent. In women, lung cancer rates declined by 1.2 percent a year, while the incidence of breast cancer, which is associated with obesity, was flat.
"Breast cancer incidence did drop when hormones were stopped, but it has now plateaued," said Dr. Powel Brown, chairman of clinical cancer prevention in the department of breast medical oncology at the University of Texas MD Anderson Cancer Center in Houston.
He was referring to the discovery several years ago that hormone replacement therapy for menopausal women increased the risk of breast cancer and heart disease.
Dr. Brown also explained that lung cancer trends for women have lagged those of men by about 10 years, reflecting the widespread use of tobacco by women.
Smoking is responsible for about a third of all cancer cases in the United States, while another 20 percent or more are tied to obesity and inactivity.
More than a third of Americans are overweight and more than a quarter are obese, increasing their chances of developing health problems such as heart disease, stroke, diabetes, as well as certain types of cancers.
Possible mechanisms for obesity's association to cancer include hormone production, the role of fat cells in tumor growth and levels of inflammation.
The annual report found that rates of pancreatic cancer and kidney cancer - both linked to excess weight and sedentary lifestyle - rose 1.1 percent and 3 percent, respectively, each year from 2004 to 2008.
The incidence of colorectal cancer, also linked to obesity, fell 2.4 percent a year over the same period.
"Part of that may be related to colorectal screening," said Dr. Brown. "It may also be related to diet or other exposures that people have. We don't understand it well."
The report also found that, overall, fewer people are dying from cancer. U.S. cancer mortality fell 1.6 percent annually from 2004 to 2008 as treatments improved and incidence dropped.
"While smoking has been considered an extreme risk factor for cancer ... in the future it will be appreciated that obesity and lack of physical activity are major risk factors," Dr. Brown said. "People need to be counseled to increase exercise, eat healthfully and lose weight."
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