Mammography - The Hidden Downside, Part III
False Negatives
Mammograms can and do sometimes miss cancers entirely. A woman may have a normal mammogram at one screening but still develop a so-called “interval cancer” before her next examination. As we have seen in our previous newsletters, this kind of cancer tends to be the most deadly. The “false negative” rate - that is, the rate at which mammography gives a clean bill of health to those who in reality do have cancer, has been estimated to be somewhere between 10 and 15 percent (Welch 2004).
The Problem of DCIS
Meanwhile, the number of cases of premalignant, non-invasive lesions such as ductal carcinoma in situ (DCIS) being diagnosed by mammography has increased by 900 percent in the US over the past 20 years. It has now reached the point where almost 20 percent of all breast cancer diagnoses involve DCIS.
Some people interpret this as a good thing, i.e., a sign that cancer is being caught in its earliest stages. Treated early or late, DCIS has a low mortality rate (around 1 percent). Precisely what percentage of these latent, precancerous lesions might eventually progress to become truly invasive is unknown, although it has been estimated that almost 50 percent of all ‘in situ’ cancers will never progress and would be better left undetected and therefore untreated (Handler 2003).
Perhaps one day in the future there will be a way of distinguishing between those women whose DCIS poses an imminent threat of invasiveness and those whose lesions are harmless, so that treatment can be directed only towards those who truly need it. Currently, though, such a test does not exist.
Undoubtedly mammography is having the effect of labeling a substantial number of women as having breast cancer, and channeling them towards aggressive treatment, when in fact they have a pseudodisease - i.e., a benign condition that poses no threat to life.
In one large-scale Canadian study of screening mammography it was found that DCIS was diagnosed in more than double the number of women who were given mammography than in those given careful clinical breast examinations (CBE) by qualified providers (i.e., 71 such women in the mammography group compared with 29 in the breast examination group). Another large Canadian study found that 71 mammography patients were given a diagnosis of DCIS compared with only 16 in the breast examination group. Meanwhile, a careful analysis of the outcomes of both these studies concluded that mortality rates from breast cancer were unaffected by screening mammography: the women in these studies experienced no survival benefit whatsoever from mammography even after 10 years of follow up (Miller 2000).
Radiation and Other Hazards
Another important factor that is largely ignored by the medical profession and the media is the radiation danger inherent in screening mammography, particularly to younger women (i.e., women in the premenopausal age range of 40-50 years). Breast tissue is highly sensitive to radiation: an annual exposure to 1 cGy, or centigray (the dosage involved in taking a standard mammogram) increases the risk of cancer by 1 percent, and over a 10-year period of annual mammography screening this could augment a woman’s cancer risk by 10 percent. The risk may be even greater - up to a 20 percent increased risk - for those women who carry certain genetic mutations (Swift 1994).
In addition, annual mammography exposes the breast tissue to repeated doses of low-energy X rays. Contrary to what one might expect, low-energy X rays are actually more damaging to DNA than their high-energy counterparts, according to a study performed at Columbia University’s Center for Radiological Research (Brenner 2002).
For younger women in particular, whose breasts are denser and who have a longer projected lifespan ahead of them than postmenopausal women, the additional exposure to X-rays posed by annual mammography beginning at the recommended age of 40 could pose a significantly increased risk of cancer. The Columbia University article concluded:
“There is evidence that low energy X rays as used in mammographic screening produce an increased biological risk per unit dose relative to higher energy photons. At low doses, the increased risk appears to be of a factor of 2. For older women, the benefit is still likely to outweigh the radiation risk. For women less than 50 years of age, however, this increase in the estimated radiation risk might indicate a somewhat later age than currently suggested, by about 5-10 years, at which to recommend commencement of routine breast screening” (Brenner 2002).
This paper is significant - and unusual - in that it both acknowledges the risks involved in repeated radiation exposure to the breast through mammography and urges a re-examination of current recommendations concerning the appropriate age to begin regular screening. Most discussions of mammography are not as frank.
Another hidden hazard in mammography is the physical compression of the breasts that is necessary to obtain a readable radiographic image. This physical compression can result in the rupture of small blood and lymphatic vessels, which, if they are in close proximity to a tumor - even a tiny tumor - may result in the release of malignant cells into the general circulation (Rosser 2000).
The Mammography Paradox
That mammography is not as effective in saving lives as its promoters have insistently claimed is bad enough, but more alarming by far is the little-publicized fact that in women aged 40-49, mammography is actually associated with an increased, rather than a decreased, risk of death - a phenomenon known to researchers as the “mammography paradox”.
Yes, you read that right: mammography in younger women (ages 40-49) may actually accelerate, rather than reduce, breast cancer mortality.
This increased death rate from breast cancer in younger women who undergo screening mammography has been documented consistently in screening trials across different countries, settings and populations. It is a fact known to many researchers in the field, yet it remains largely unknown to the general public - and it certainly not a danger of which women are routinely made aware by their healthcare providers.
One critic of exclusive reliance on screening mammography is Cornelia J. Baines, MD., of the University of Toronto. Dr. Baines is hardly an outsider to the field. She is deputy director of the prestigious Canadian National Breast Screening Study, and the author of 70 PubMed-listed journal articles. She has also written an important paper that is frank in its discussion of this issue. In this paper, aptly titled ‘Mammography screening : Are women really giving informed consent?’ Dr. Baines says: “Many women remain unaware of the extent to which efforts to achieve breast cancer control through mammography screening may be doing harm as well as good. An unacknowledged harm is that for up to 11 years after the initiation of breast cancer screening in women aged 40-49 years, screened women face a higher death rate from breast cancer than unscreened control women, although that is contrary to what one would expect: (Baines 2003).
How could this happen? How can it be that instead of saving their lives, earlier detection might actually result in a greater likelihood of death in these women?
- Ralph W. Moss, Ph.D.
