Cancer screening as we age

Experts have battled over whether women should start getting screening mammograms for breast cancer at age 40 or 50. Hit the half-century mark these days, and chances are that your doctor will hand you a referral for a colonoscopy. Women start getting Pap smears to test for cervical cancer when they turn 21 or even sooner, depending on when they become sexually active. But now attention — and with it, controversy — is shifting to questions about at what age people should be when they stop getting these and other important screening tests.

Pressure seems to be building to push the age limits for screening tests into people's late 70s and 80s — even their 90s. There are a number of reasons for this. Americans are living longer, so there are more years of life to save if a treatable cancer is found. Cancer treatment is more tolerable than it used to be, so treatment is a more realistic option for older people.

Opening a Pandora's box

But expanding screening to include older people may also have some serious drawbacks. Many of the cancers we screen for become more common with age, so screening elderly people is bound to find more cancers. Cancer in older people often tends to grow and spread slowly, if at all. So screening programs that include the elderly could mean diagnosis and treatment of a lot of cancers that aren't causing any real harm and weren't likely to in the future. When you factor in the extra testing and the false positives, we could be opening up a Pandora's box of medical intervention.

There are treatment issues, too. Notwithstanding the recent advances, if a serious cancer is found, it may be more difficult to treat in many older people because of other conditions they have.

Right now, there are more questions than answers about cancer screening in older people. Here is a brief rundown on age-related issues for four screening tests for important cancers:

Breast cancer

The American Cancer Society sets no age limits on mammograms, recommending that women get the exams every year as long they are in good health. In the absence of research that addresses the issue of mammography in older women head-on, researchers have conducted several studies that have examined the question in a roundabout way by categorizing older women who have been diagnosed with breast cancer by how often they got mammograms before their diagnosis. For the most part, the results have been "pro-mammogram." Researchers have found that women who have gotten mammograms regularly are more likely to have their cancer diagnosed at an earlier stage than women who have gotten mammograms infrequently or not at all.

It's hard not to be impressed by the growing number of studies that suggest older women should get mammograms regularly. And yet part of the math of mammography — indeed, any screening test — is that it will generate extra diagnostic testing. The cost, inconvenience, and anxiety caused by the diagnostic tests must be weighed against finding and treating early-stage breast cancer.

Cervical cancer

Of all the screening tests, the Pap smear for cervical cancer is the one closest to having an agreed-upon age cutoff. The American Cancer Society says women who are 70 or older who have had three or more normal Pap tests in a row and no abnormal test results in the past 10 years can choose to stop having the test.

It's safe for older women with a history of normal Pap smears to stop getting screened for a couple of reasons. Cervical cancer originates with infection with the human papillomavirus (HPV). But it takes years, even decades, for cervical cancer to develop from the cellular abnormalities caused by the virus. Moreover, older women rarely contract new HPV infections. Even if they were to do so, a new infection isn't likely to develop into cervical cancer in their lifetime.

Colon cancer

Colon cancer screening in older people is largely a blank slate. The American Cancer Society and other groups are silent on the subject and don't set any kind of age cutoff.

Although there are other ways to screen for colon cancer, colonoscopy has taken off since Medicare started covering it in 2001. With the heavy-duty laxative preparation needed to clean out the colon before the exam and the sedation used during it, there's much more involved in getting a colonoscopy than the other cancer screens. Studies have found colonoscopies done on older people (usually defined as ages 75 and up) take longer, are less likely to yield a complete view of the colon, and, most troubling of all, are more likely to result in perforations of the colon.

Prostate cancer

Screening men for prostate cancer at any age is controversial. The government's Preventive Services Task Force sent out mixed signals in its 2002 recommendation, saying that the prostate-specific antigen (PSA) test can detect early-stage cancer but also leads to frequent false positives and unnecessary anxiety and biopsies. It concluded that the evidence is "insufficient" to decide whether the benefits outweigh the harms. The American Cancer Society has come down in favor of PSA testing and digital rectal examination for men starting at age 50, but it also hedged its bets. The recommendation is that the tests be offered to men, and only to those who have at least a 10-year life expectancy.

There's good reason to be even more skeptical about the value of PSA screening in older men. Many older men have prostate cancer that causes no illness. Furthermore, the forms of prostate cancer that the PSA test helps find in elderly men are often slow-growing. Many of the tumors wouldn't cause any symptoms for years — if ever.

A big part of the problem with the PSA test is the number of false positives. By one estimate, 75% of the men who have had a prostate biopsy because of a high PSA level (4.0 to 10.0 nanograms per milliliter) don't have cancer.

August 2008 update

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