Medicine is perhaps the most inexact of all sciences, and nowhere is this more evident than in the realm of cancer screening. For most cancers, by the time you notice something is awry -- an uncomfortable growth, bone pain, a persistent cough -- the cancer has spread, and your chances of survival are greatly reduced. So it seems like common sense that the earlier and more often you screen for cancer, the better your chances of beating the disease.
Think again. Plenty of physicians question the usefulness of some of the most frequently administered diagnostic tests. They even disagree about whether early detection of some cancers will make any difference to the patient's survival. Only one test, for cervical cancer, has proven to be a clear win. This deadly cancer has been almost eliminated since the advent of routine pap smears in the 1950s.
The problem is that our bodies are likely riddled with minuscule tumors. Most are harmless and will probably stay that way. Others may grow, but so slowly that they never pose a threat. Plus, your immune system vanquishes tiny malignancies every day. Yet as screening becomes more accurate, these tiny tumors can be detected, setting off a cascade of costly and possibly dangerous procedures such as biopsies, surgeries, and chemo.
That's why virtually every cancer specialist is opposed to full-body CT scans. These high-resolution pictures can reveal all kinds of growths that rarely threaten health. But once detected, an odd-looking clump of cells is hard to ignore, and patients can quickly face a spiraling number of medical decisions over what could be a non-issue.
Most tests are more useful, depending on your risk factors. Everyone, of course, is at some risk -- the American Cancer Society estimates that one in three people will develop the disease. About 5% of all cancers are inherited, but the rest are caused by a mix of genetic mistakes and environmental factors such as tobacco smoke, excessive sunlight, or diet.
The biggest risk factor is age. The longer we live, the greater the likelihood that malfunctioning genes will trigger out-of-control cell growth. That's why cancer is the leading cause of death for men age 60 to 79 but comes in fifth among causes for those 20 to 39. Consequently, most cancer specialists say the magic number for cancer screening is 50, the age when most standard tests are recommended. High-risk patients may want to start earlier. But keep in mind that no test is 100% accurate -- and that standard recommendations may not be your best course.
-- COLON CANCER
Colon and rectal cancer kill some 60,000 Americans each year, and oncologists believe these deaths could largely be avoided with early detection. A colonoscopy, in which a physician inserts a lighted tube and camera through the entire colon to look for diseased tissue, is both accurate and safe.
It can also be preventive. If the doctor sees polyps that are often precursors to cancer, they can be removed during the procedure. If none are found, a second colonoscopy isn't necessary for 5 to 10 years. "Colon screening should be high on the list of things everyone should be doing," says Dr. Victor Gann, professor of medicine at Columbia University. Unfortunately, everyone isn't. A study just reported by Dartmouth Medical School found that more U.S. men are screened for prostate than for colon cancer, even though the prostate screening test has not been proven to reduce cancer deaths, while screening for colon cancer has.
-- PROSTATE CANCER
The test for prostate cancer is a bad combination of high sensitivity and low specificity. A blood test measures an enzyme called prostate-specific antigen (PSA), which rises when the prostate is enlarged. However, PSA can rise for all kinds of reasons, so the test produces a high percentage of false positives, triggering unnecessary biopsies.
In addition, this is often one of the slowest-growing of all cancers -- it is frequently said that more men die with prostate cancer than from it. Thus, PSA tests for men in their 70s and 80s are often considered irrelevant. For men in their 50s or those at high risk, it can be more useful. The U.S. Preventive Services Task Force (USPSTF), a federal advisory board, says there is insufficient evidence to recommend for or against routine prostate cancer screening, and the American Medical Assn. advises that patients interested in the test should be informed of the potential for harm as well as benefit. "But in the era of assembly-line medicine, you don't have time to do that," says a New York area internist. "Most internists I know order the test because it's easier to give patients what they ask for."
-- BREAST CANCER
There is also no definitive answer about the usefulness of breast-cancer screening. The USPSTF recommends mammograms every one to two years for women 40 and over, but cancer specialists acknowledge that there is no data proving that the test saves lives. There are more treatment options when breast cancers are detected early, however, so specialists see little downside. A newer test called ductal lavage involves extracting a few cells from the nipple area and examining them for atypical cells. If abnormalities are detected, a woman's risk of breast cancer increases fivefold.
-- LUNG CANCER
Lung cancer kills more people every year than colon, prostate, and breast cancer combined, and it's easy to determine who's at risk: 95% of lung-cancer victims are smokers or ex-smokers. If you fall into that category, you can have an annual X-ray, but by the time most tumors are detectable, they're usually too large to be successfully treated. A new test called a spiral CT scan is more accurate -- and expensive. A scan can run $500 or more, vs. $50 for an X-ray, and few insurers cover it. The technology spirals low-dose X-rays around the body as the patient is transported through a metal tube. Studies have found the spiral CT vastly better than X-rays at detecting tumors that are still small enough to treat, but the scans also produce far more false positives, leading to unnecessary biopsies. And there's no proof that early detection extends survival.
Ultimately, consumers must keep in mind that no test promises safe passage, whatever the result. But if you're over 50 and haven't had any, talk to your doctor. A test might not save your life -- but then again, it just might. By Catherine Anst