Many people worry that cancer is more common than it used to be -- that we’re experiencing a cancer epidemic of sorts. It's easy to understand why they feel this way, with cases of cancer cropping up all around them and affecting people they know. But the statistics suggest otherwise.
The Annual Report to the Nation on the Status of Cancer for 2009 found that cancer incidence rates (or the rates at which new cancers are diagnosed based on the size of the population) have stabilized and, for many of the most common forms of cancer, are actually dropping. Among men, incidence rates for lung cancer (the leading cause of cancer death in men) have recently decreased by 1.8% a year, and rates for colorectal cancer have fallen by roughly 3% annually. Perhaps most impressive were the changes in the incidence of breast cancer, the second-leading cause of cancer death in women, behind lung cancer. Those rates have dropped by approximately 2% a year.
Cancer experts can't pinpoint exactly what is responsible for these encouraging trends, but they have a pretty good idea of what may be influencing some of them. The decrease in lung cancer cases is clearly related to the fact that fewer people are smoking than in the past. Less smoking means less risk.
The recent decline in breast cancer cases may also be tied to a widespread reduction in risk. The biggest driver is probably the decreased use of hormone replacement therapy in post-menopausal women. In 2002, the Women's Health Initiative found that the long-term use of replacement therapy increased a woman's risk of breast cancer. Since the study's release, the use of the therapy has fallen substantially.
For other types of cancers, screening appears to have had an effect. Though tests for cancer are generally used to detect malignancies in their earliest stages, some can actually help avert their development. Sigmoidoscopy and colonoscopy, for example, detect polyps in the colon that can go on to become cancerous. Removing these cancer precursors during routine screenings greatly diminishes the possibility of developing cancer.
Pap smears protect against cervical cancer in a similar way. These screening tests identify pre-malignant abnormalities which, when detected and treated early, nearly eliminate the risk of cancer.
In spite of the largely encouraging cancer trends, the news isn't all good. Cancers of the thyroid, bladder and kidney as well as certain forms of leukemia and lymphoma are on the rise in women; among men, cancers of the liver, kidney and esophagus are increasing. In some cases, little is known ‘about the cause for these upswings; in others, it’s less mysterious. With liver cancer, alcohol abuse and hepatitis C infection play a role; improved diagnostic tests are probably partially responsible for the uptick in thyroid cancer, because they detect cases that in the past would not have been found.
Though overall cancer rates are falling in the U.S., the absolute number of cases of cancer is expected to rise. Most of that has to do with age and sheer numbers. We’re an aging and growing population in the United States: There are simply more people at greater risk for developing disease.
Cancer Trends Progress Report (National Cancer Institute)
State Cancer Profiles (National Cancer Institute)
Cancer Data and Statistics (Centers for Disease Control)