Mammography

Mammography  (medical procedure)

Dr. Peter Gøtzsche explains why mammography is a Big Pharma racket

Official narrative

Mammograms play a key role in breast cancer screening. They can detect breast cancer before it causes signs and symptoms. Mammograms have been shown to reduce the risk of dying of breast cancer.

Risks

The use of mammography as a screening tool for the detection of early breast cancer in otherwise healthy women without symptoms is controversial.

Keen and Keen indicated that repeated mammography starting at age fifty saves about 1.8 lives over 15 years for every 1,000 women screened. This result has to be seen against the adverse effects of errors in diagnosis, over-treatment, and radiation exposure. The Cochrane analysis of screening indicates that it is "not clear whether screening does more good than harm". According to their analysis, 1 in 2,000 women will have her life prolonged by 10 years of screening, while 10 healthy women will undergo unnecessary breast cancer treatment. Additionally, 200 women will suffer from significant psychological stress due to false positive results. Newman points out that screening mammography does not reduce death overall, but causes significant harm by inflicting cancer scare and unnecessary surgical interventions. The Nordic Cochrane Collection notes that advances in diagnosis and treatment of breast cancer may make breast cancer screening no longer effective in decreasing death from breast cancer, and therefore no longer recommend routine screening for healthy women as the risks might outweigh the benefits.

Often women are quite distressed to be called back for a diagnostic mammogram. Most of these recalls will be false positive results. Of every 1,000 U.S. women who are screened, about 7% will be called back for a diagnostic session (although some studies estimate the number to be closer to 10% to 15%). About 10 of these individuals will be referred for a biopsy; the remaining 60 cases are found to be of benign cause. Of the 10 referred for biopsy, about 3.5 will have cancer and 6.5 will not. Of the 3.5 who have cancer, about 2 will have an early stage cancer that will be cured after treatment.

Mammography may also produce false negatives. Estimates of the numbers of cancers missed by mammography are usually around 20%. Reasons for not seeing the cancer include observer error, but more frequently it is because the cancer is hidden by other dense tissue in the breast, and even after retrospective review of the mammogram, the cancer cannot be seen. Furthermore, one form of breast cancer, lobular cancer, has a growth pattern that produces shadows on the mammogram that are indistinguishable from normal breast tissue.

Mortality

The Cochrane Collaboration states that the best quality evidence does not demonstrate a reduction in mortality or a reduction in mortality from all types of cancer from screening mammography.

The Canadian Task Force found that for women ages 50 to 69, screening 720 women once every 2 to 3 years for 11 years would prevent one death from breast cancer. For women ages 40 to 49, 2,100 women would need to be screened at the same frequency and period to prevent a single death from breast cancer.

Women whose breast cancer was detected by screening mammography before the appearance of a lump or other symptoms commonly assume that the mammogram "saved their lives". In practice, the vast majority of these women received no practical benefit from the mammogram. There are four categories of cancers found by mammography:

1. Cancers that are so easily treated that a later detection would have produced the same rate of cure (women would have lived even without mammography).
2. Cancers so aggressive that even early detection is too late to benefit the patient (women who die despite detection by mammography).
3. Cancers that would have receded on their own or are so slow-growing that the woman would die of other causes before the cancer produced symptoms (mammography results in over-diagnosis and over-treatment of this class).
4. A small number of breast cancers that are detected by screening mammography and whose treatment outcome improves as a result of earlier detection.

Only 3% to 13% of breast cancers detected by screening mammography will fall into this last category. Clinical trial data suggests that 1 woman per 1,000 healthy women screened over 10 years falls into this category. Screening mammography produces no benefit to any of the remaining 87% to 97% of women. The probability of a woman falling into any of the above four categories varies with age.

False positives

The goal of any screening procedure is to examine a large population of patients and find the small number most likely to have a serious condition. These patients are then referred for further, usually more invasive, testing. Thus a screening exam is not intended to be definitive; rather it is intended to have sufficient sensitivity to detect a useful proportion of cancers. The cost of higher sensitivity is a larger number of results that would be regarded as suspicious in patients without disease. This is true of mammography. The patients without disease who are called back for further testing from a screening session (about 7%) are sometimes referred to as "false positives". There is a trade-off between the number of patients with disease found and the much larger number of patients without disease that must be re-screened.

Research shows that false-positive mammograms may affect women's well-being and behavior. Some women who receive false-positive results may be more likely to return for routine screening or perform breast self-examinations more frequently. However, some women who receive false-positive results become anxious, worried, and distressed about the possibility of having breast cancer, feelings that can last for many years.

False positives also mean greater expense, both for the individual and for the screening program. Since follow-up screening is typically much more expensive than initial screening, more false positives (that must receive follow-up) means that fewer women may be screened for a given amount of money. Thus as sensitivity increases, a screening program will cost more or be confined to screening a smaller number of women.

Overdiagnosis

The central harm of mammographic breast cancer screening is overdiagnosis: the detection of abnormalities that meet the pathologic definition of cancer but will never progress to cause symptoms or death. Dr. H. Gilbert Welch, a researcher at Dartmouth College, states that "screen-detected breast and prostate cancer survivors are more likely to have been over-diagnosed than actually helped by the test." Estimates of overdiagnosis associated with mammography have ranged from 1% to 54%. In 2009, Peter C. Gotzsche and Karsten Juhl Jørgensen reviewed the literature and found that 1 in 3 cases of breast cancer detected in a population offered mammographic screening is over-diagnosed. In contrast, a 2012 panel convened by the national cancer director for England and Cancer Research UK concluded that 1 in 5 cases of breast cancer diagnosed among women who have undergone breast cancer screening are over-diagnosed. This means an over-diagnosis rate of 129 women per 10,000 invited to screening.

False negatives

Mammograms also have a rate of missed tumors, or "false negatives". Accurate data regarding the number of false negatives are very difficult to obtain because mastectomies cannot be performed on every woman who has had a mammogram to determine the false negative rate. Estimates of the false negative rate depend on close follow-up of a large number of patients for many years. This is difficult in practice because many women do not return for regular mammography making it impossible to know if they ever developed a cancer. In his book The Politics of Cancer, Dr. Samuel S. Epstein claims that in women ages 40 to 49, one in four cancers are missed at each mammography. Researchers have found that breast tissue is denser among younger women, making it difficult to detect tumors. For this reason, false negatives are twice as likely to occur in pre-menopausal mammograms (Prate). This is why the screening program in the UK does not start calling women for screening mammograms until age 50.

The importance of these missed cancers is not clear, particularly if the woman is getting yearly mammograms. Research on a closely related situation has shown that small cancers that are not acted upon immediately, but are observed over periods of several years, will have good outcomes. A group of 3,184 women had mammograms that were formally classified as "probably benign". This classification is for patients who are not clearly normal but have some area of minor concern. This results not in the patient being biopsied, but rather in having early follow up mammography every six months for three years to determine whether there has been any change in status. Of these 3,184 women, 17 (0.5%) did have cancers. Most importantly, when the diagnosis was finally made, they were all still stage 0 or 1, the earliest stages. Five years after treatment, none of these 17 women had evidence of re-occurrence. Thus, small early cancers, even though not acted on immediately, were still reliably curable.

Radiation

The radiation exposure associated with mammography is a potential risk of screening, which appears to be greater in younger women. A study of radiation risk from mammography concluded that for women 40 years of age and older, the risk of radiation-induced breast cancer was minuscule, particularly compared with the potential benefit of mammographic screening, with a benefit-to-risk ratio of 48.5 lives saved for each life lost due to radiation exposure. However, this estimate is based on modelling, not observations. In contrast epidemiologic studies show a high incidence of breast cancer following mammography screening. Organizations such as the National Cancer Institute and United States Preventive Task Force do not take such risks into account when formulating screening guidelines.

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