Rethinking the benefits of breast and prostate cancer screening

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For two decades, the public-health message has been that cancer screening saves lives. In some cases, especially with cancers of the cervix and colon, screening does, in fact, work as it should: sniffing out disease at its earliest and most curable stages. But for breast and prostate cancers—two of the most widespread in the U.S.—the benefits of screening are more complicated.

Consider that the average American’s risk of being diagnosed with prostate cancer or breast cancer has doubled since 1980 because screening detects cancers earlier than ever before. Over the same time period, however, the rate of death due to breast and prostate cancer has barely budged. Over the years, that disconnect has raised red flags among experts, even while most Americas continued to believe (because they are told) that screening would protect them from death.

This week the conversation garnered national attention when physicians at the University of California, San Francisco, and University of Texas, San Antonio, published an analysis in the Journal of the American Medical Association expounding on their concerns about the ongoing harm inflicted on patients who undergo prostate and breast cancer screening. One problem is that screening often picks up harmless or non-life-threatening tumors that could have gone unnoticed for a lifetime, leading to unnecessary and aggressive treatment for patients. In the days before widespread mammography, for instance, physicians rarely encountered ductal carcinoma in situ (or DCIS), a type of low- to intermediate-grade breast cancer that grows slowly and may even regress, meaning that the body may rid itself of the tumor. But today DCIS accounts for nearly 30 % of all breast cancer diagnoses (more than 60,000 cases a year), leading to an untold amount of treatment and patient distress.

Similarly, with prostate cancer, diagnoses skyrocketed with the advent in the 1980s of the prostate-specific antigen (PSA) test, which uses protein levels in the blood to gauge a man’s risk of prostate cancer. “More than a million more men were diagnosed with prostate cancer in the last quarter century, whose cancer would have gone undetected in the early ’70s,” writes Gil Welch, MD, a professor at Dartmouth Medical School, in his book  Should I Be Tested for Cancer? What’s more, most men with an elevated PSA level turn out not to have cancer; according to the National Cancer Institute, only 25% to 35% of men who have a biopsy due to a PSA test actually have the disease.

Another significant drawback of both breast and prostate cancer screening is that the tests often miss the most lethal, fast-growing cancers, capable of rearing up between screenings. And, even when screening does nab these cancers, patients frequently die anyway. “It is disappointing that the absolute numbers of more advanced disease have not decreased nearly as much as hoped for either cancer,” write the authors of the JAMA article.

When screening picks up a minor tumor, the patient’s situation gets even more complx: Should you act now or take a wait-and-see approach? The phrase “wait and see” is a tough pill to swallow on the heels of the word cancer. So, what often follows is overtreatment. For women, the researchers suspect the rate of breast cancer overdiagnosis (finding a potentially harmless tumor) is as high as 1 in 3 for non-invasive cancers, such as DCIS. Patients with these diagnoses are sent down a slippery slope toward surgery, radiation, and possibly even chemotherapy. “We may be harming anyone with DCIS,” says lead-author Laura Esserman, MD, a professor of surgery and radiology at the University of California, San Francisco’s Comprehensive Cancer Center.

The outcome is similar for many men diagnosed with slow-growing and non-life-threatening prostate cancer, which is often aggressively overtreated. The fix, including surgery and radiation, leaves many men with urinary problems, loss of sexual function or both.

Still, the JAMA authors point out that mortality has decreased for both breast and prostate cancers during the past 20 years, but they note that it’s not clear how much of that is thanks to screening. In the end, the authors say they support screening but want to see it used more judiciously. For instance, says Esserman, clinicians should think more about who should not get a mammogram, such as women over the age of 70. These women are the most likely to develop low-risk cancers, she explains, and they are also most likely to die of something else unrelated to their cancer. At the same time, doctors should be screening women in the highest-risk categories even more, she says. “When we first started screening we thought early detection would dramatically fix the problem. Today we know that screening has value, but we need to understand what it can and cannot do. There is a lot of uncertainty in medicine, but we shouldn’t let that lead to more intervention. Less screening isn’t necessarily a bad thing.”

So, where does this leave you? Welch spells it out neatly in his book. Essentially, mammography reduces the odds of a 60-year-old woman dying of breast cancer in the next decade by 30%. Sounds impressive, until you look at her absolute risk: by getting her annual mammogram, her chances of dying from breast cancer are whittled from 0.9% to o.6%. Overall, for every 1,000 women in their 60s screened for breast cancer in the next 10 years, mammograms will save the lives of 3 people but 6 others will still die. (The numbers edge up or down in lockstep with a woman’s age.)

For its part, the American Cancer Society (ACS) continues to recommend that women 40 and older get an annual mammogram and that men discuss the risks and benefits of PSA screening with their doctors. But the ACS also concedes that the benefits of early screening may be overstated and says it will take a hard look at its public-health message.

Esserman’s advice for patients diagnosed with a slow-growing or early-stage cancer is not to rush into treatment. “The most important thing to ask your physician is: will this cancer kill me?”  Of course, that is often the most difficult question to answer. But, “if the answer is probably not,” says Esserman, “weigh the treatment pros and cons carefully before taking the next step.”

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