Does Screening Mammography Save Lives?

The benefits of regular mammograms may be overblown, one expert argues.


May 21, 2007— -- Breast cancer is a topic that seldom evokes dispassionate, let alone objective, treatment.

There is good reason for that. We all know, often intimately, of the tragedy this cancer can cause.

Furthermore, the topic roils with gender issues and other issues of bias in the provision of health care. No one should be deprived of effective care of the highest quality for any reason, including gender and ethnicity. We need to address past wrongs.

However, past wrongs and current tragedies do not excuse providing remedies that are ineffective. It is under this banner that I want us to calmly and objectively examine the effectiveness of screening mammograms. I have done so before, in detail in "Last Well Person." I do so today because of the chest-pounding about the decrease in the numbers of women submitting to mammograms and the auguring about a consequent rebound in breast cancer incidence.

First, let me make certain we all understand what is meant by "screening mammography."

Screening is a public health initiative. It is advised that all women of a certain age should submit to mammography periodically, regardless of whether or not they have any particular personal concerns.

The rationale is that screening will lead to more good than harm for the public at large by identifying those women who are unaware of a treatable breast cancer.

Women who forego screening can still turn to a physician with any concern, such as feeling a lump or nipple discharge. The physician may even order a mammogram to decide whether or where to biopsy. That is not a screening mammogram; that is mammography used as diagnostic test for a specific reason in a particular patient.

Back to screening mammography: Let me tell you about the women of Malmö, Sweden. In 1976, half of the women between the ages of 44 and 68 were randomly selected and invited to participate in mammographic screening every 18 to 24 months for a decade. All the women -- both the screened and unscreened -- were followed for another 15 years after that decade.

Over these 25 years, 9,279 of the 21,000 in the invited group, and 9,514 of the 21,000 in the control group, died of various causes.

In total, 1,320 women in the invited group were diagnosed with breast cancer, and 212 died from the disease. Breast cancer was detected in 1,205 women in the study's control group who did not get routine screening, and 274 of those women died from their breast cancer.

The difference between the two groups is not considered statistically significant. So whether or not women received screening mammography did not seem to affect the chances of their doctor detecting a breast cancer, regardless of their age.

Randomized, controlled trials of screening mammography from Canada and Stockholm have results similar to the Malmö trial.

Could this be? Screening mammography is an inalienable rite of passage, a mantra for "health promotion, disease prevention" and an industry. Have we been deluding ourselves?

Maybe trials such as the Malmö trial are asking the wrong question. We don't screen to find cancer. We screen to find the cancer that would kill a woman before her time unless it is detected early and treated appropriately.

Perhaps screening detects some breast cancers early enough so that a woman can live long enough to die of something else, or even die later of breast cancer. There is a hint that such a benefit was afforded the women of Malmö who ranged in age from 55 to 69 when the study began. For every 250 women screened for a decade, one breast cancer death was prevented.

Do you think this justifies screening? I have doubts that we can even reliably and reproducibly discern such a small benefit.

Many a mammogram will be read as suspicious, and many as suggestive of cancer. For most of the former and all the latter, women are subjected to biopsy. If the biopsy documents nothing evil, the mammogram is a false positive.

For the women whose suspicious mammogram was a false positive, for the women who were found to have noninvasive cancer on biopsy, for the women who were found to have cancer that would not have caused them grief in their lifetime, and for the women who are treated for invasive cancer when some other disease proves their reaper, mammographic screening is an exercise in overdiagnosis and overtreatment.

"Suspicious" and "suggestive" are in the eyes of the beholder; false positive rates vary dramatically from country to country and, to some extent, from reader to reader.

In the United States, radiologists are so hesitant to read a mammogram as "normal" that false positive rates can reach 80 percent. The more sensitive mammographic techniques, such a digital or magnetic resonance imaging, result in higher false positive rates. This hedging on the readings is driven in no small part by the fact that "missing a breast cancer" on mammography is the most frequent reason for malpractice litigation in the United States.

Breast cancer is viewed as a plague. A "war" on breast cancer is viewed as a crusade. Screening mammography is Excalibur. Blunt or not, it's the best we have.

But screening mammography is so terribly blunt that it approaches useless: It finds very few cancers that are truly treatable, it misses many of these and it is awash in false positives.

Norway, Sweden, Australia and the United Kingdom are re-examining their national experience with screening mammography because of appraisals similar to mine.

If a woman's life was saved because of early detection of an evil breast cancer, she should thank her lucky stars rather than her mammographer. I would relegate mammograms to the archives of false starts, next to radical mastectomy.

Dr. Nortin Hadler is professor of medicine and microbiology/immunology at theUniversity of North Carolina at Chapel Hill, and an attending rheumatologist at University of North Carolina Hospitals.

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