This raises some obvious and worrisome questions: Did the x-rays and/or the sometimes torturous compression of breasts during mammography actually spur cancer to develop? Or does this just look like an increase in the disease rate because mammography is simply identifying more cases of breast cancer?
The answer to the first question is that no one knows (and it isn't addressed in the Archives of Internal Medicine study). But the second question has an unexpected and - for those interested in the human body's innate ability to heal itself - potentially paradigm-shifting answer. The researchers say they can't blame the increased incidence of breast cancer on more cases being found because the rates among regularly screened women remained higher than rates among women of the same age who only received mammograms once after six years. Bottom line: the scientists conclude this indicates that some of the cancers detected by mammography would have spontaneously regressed if they had never been discovered on a mammogram and treated, usually with chemotherapy and radiation. Simply put, it appears that some invasive breast cancers simply go away on their own, healed by the body's own immune system.
Per-Henrik Zahl, M.D., Ph.D., of the Norwegian Institute of Public Health, Oslo, and his research team studied breast cancer rates among 119,472 women (age 50 to 64). These research subjects were asked to participate in three rounds of screening mammograms between 1996 and 2001, as part of the Norwegian Breast Cancer Screening Program. The scientists then compared the number of breast cancers found in this group to the rate of malignancies among a control group of 109,784 women who were the same ages in 1992, and who would have been invited for breast screenings if the program had been in place that year. Cancers were tracked using a national registry. Then, after six years, all participants were invited to undergo a one-time screening to assess for the prevalence of breast cancer.
The researchers were surprised to find that the incidence of invasive breast cancer was 22 percent higher in the group regularly screened with mammography. In fact, screened women were more likely to have breast cancer at every age.
"Because the cumulative incidence among controls never reached that of the screened group, it appears that some breast cancers detected by repeated mammographic screening would not persist to be detectable by a single mammogram at the end of six years," the authors stated in their report. "This raises the possibility that the natural course of some screen-detected invasive breast cancers is to spontaneously regress."
The researchers also conclude that their findings "provide new insight on what is arguably the major harm associated with mammographic screening, namely, the detection and treatment of cancers that would otherwise regress."
This does not mean breast cancer should be ignored or not treated. After all, breast cancer is the second leading cause of death among American women. But the extraordinarily good and hopeful news is that it appears invasive breast cancer sometimes can be destroyed naturally -- at least in some people -- by the body's own innate defenses.
"Although many clinicians may be skeptical of the idea, the excess incidence associated with repeated mammography demands that spontaneous regression be considered carefully," the scientists wrote in their report. "Spontaneous regression of invasive breast cancer has been reported, with a recent literature review identifying 32 reported cases. This is a relatively small number given such a common disease. However, as some observers have pointed out, the fact that documented observations are rare does not mean that regression rarely occurs. It may instead reflect the fact that these cancers are rarely allowed to follow their natural course."
In an editorial in the Archives of Internal Medicine that accompanies the breast cancer study, Robert M. Kaplan, Ph.D., of the University of California, Los Angeles, and Franz Porzsolt, M.D., Ph.D., of Clincal Economics University of Ulm, Germany, wrote that the most important concern raised by the study is "how surprisingly little we know about what happens to untreated patients with breast cancer.
In addition to not knowing the natural history of breast cancer for younger women, we also know very little about the natural history for older women. We know from autopsy studies that a significant number of women die without knowing that they had breast cancer (including ductal carcinoma in situ). The observation of a historical trend toward improved survival does not necessarily support the benefit of treatment."