Cancer screening

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Debate is ongoing as to what age people should no longer be eligible for cancer screening.

Does it make sense to get a mammogram if you’re 80? A colonoscopy if you're 85? Experts are still sorting it out.

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 has a present waiting for you: a referral for a colonoscopy.

It's also a given that women will start getting Pap smears, the screening 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 how old people should be when they stop getting these screening tests.

Americans are now accustomed to getting screening tests regularly, so as they get older it's only natural that they'd wonder about how long they should continue getting these tests.

And 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 - especially when the cancer is caught early - 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. Oncologists refer to these cancers as "indolent tumors."

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, both because of the nature of the cancer and limited life expectancy.

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. Just the practical issues of getting people to their appointments and having them adhere to complicated regimens will present some challenges.

Right now, there are more questions than answers about cancer screening in older people. Open up the research cupboard and the shelves are pretty bare. Most screening studies have enrolled few, if any, people over age 75.

The good news is that this is a lively enough issue that it's now beginning to attract some research interest and dollars. The danger is that clinical practice will get ahead of the research, which has happened many times before with cancer screening.

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.

The U.S. Preventive Services Task Force, whose recommendations are the closest thing we have to official government guidelines, says pretty much the same thing: women should get mammograms annually or every other year as long as their life expectancy is not limited by other diseases - a more precise way of saying as long as they're in good health.

The American Geriatrics Society recommends that women over 75 get mammograms every two to three years as long as their life expectancy is more than four years.

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.

In 2008, researchers at the M.D. Anderson Cancer Center in Texas reported results of an analysis of data on over 12,000 breast cancer patients ages 80 and over. Like other researchers, they found an association between regular mammograms and the cancer being diagnosed at an earlier stage.

Quite reasonably, the association is presented as evidence that even women in their 80s stand to benefit from regular screening because cancers are being found at a more treatable stage.

It falls well short, though, of the gold standard for judging screening tests, which is evidence that the people who are screened live longer than those who aren't.

The M.D. Anderson study did hint at a survival advantage, although such studies are plagued by so-called healthy user bias: women who go to the trouble of doing something like getting mammograms regularly may be fundamentally healthier than women who don't. Researchers use statistical techniques to compensate for this bias, but it's difficult to weed out entirely.

Despite these qualms, it's hard not to be impressed by the growing number of studies that suggest older women should get mammograms regularly.

Dutch investigators presented findings in 2008 that showed women between the ages of 75 and 79 were less likely to die from breast cancer if they had continued to get mammograms regularly through age 75.

And yet part of the math of mammography - indeed, any screening test - is that it will generate extra diagnostic testing. The National Cancer Institute estimates that 85 out of every 1,000 women over age 65 who have a mammogram will be referred for diagnostic tests, and out of those 85, only nine will have cancer. 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.

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