Tuesday 25th February 2020


Woman undergoing a mammogram of the right breast

Woman Undergoing a Mammogram of the Right Breast

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Cancer Screening

A mammogram, or mammography, is a test to detect if there are any early signs of breast cancer in presumably healthy women who have no symptoms of breast cancer.

A mammogram, used to screen for breast cancer and detect the disease at a very early stage, is an X-ray image of breast. During a mammogram, each breast is carefully compressed between two solid surfaces to spread out the breast tissue, and an x-ray is taken, capturing usually two black-and-white photographs of each breast. Doctors will then analyze the x-ray and interpret its results to detect any changes in breast tissue which are too small to be noticed or felt by the woman or a doctor but may indicate cancer.

Breast screening is part of the broader procedure of cancer screening, so let's look at this first.

Lots of people have severe diseases but do not know it as they have no symptoms. Screening is the process of administering tests to a symptomless group of people or population to diagnose illness at an early stage.

A screening practice can only be successful, first, if the test used can distinguish between those who have the disease and those who do not and, second, if there is availability of an effective treatment curing the disease or stopping its progression.

No screening test can be perfect: all produce false positives, diagnosing a disease when it is not there, and false negatives, not diagnosing a disease when it is there. Even an imperfect test, however, can be useful if the benefits of early diagnosis outweigh the damages created by wrong results.

Cancer screening is advocated on the basis of the supposition that an early diagnosis in a presymptomatic stage of the illness increases the probability that the cancer can be cured. This supposition is not always true: if it can be cured depends on the type of cancer and on whether it metastasises early, i.e. it spreads early to other organs or tissues of the body, or not. The nature of this growth has far more capability to predict the outcome than the time, early or late, of the diagnosis.

Good tests have both high positive and high negative predictive value, they can answer the question: 'Does this person have the disease or not?' Unfortunately, there is a trade off between false negatives and false positives, that is, the more accurate a test is in not missing real cancers (test sensitivity) the more it will overdiagnose cancer in healthy people (test specificity), and vice versa the introduction of more restrictive criteria for the definition of a positive test result reduces the rate of false positives but also increases the rate of false negatives. This is the case for mammograms.

In addition, a test will have a higher predictive value if the incidence (or frequency) of the disease in question is higher among the people who are screened. In the case of cancer screening, that incidence is low.


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Breast Screening

Worlwide, breast cancer is the second most commonly diagnosed cancer after lung cancer, and the fifth cancer in terms of mortality.

Breast cancer is in several developed countries, like the USA and the UK, the most common cancer in women, although not the most deadly, lung cancer being the one with the highest mortality even among women.

Women's deadliest illness in developed countries anyway, by a vast margin, is cardiovascular disease, killing several times as many women as breast cancer.

This article is not about mammography, the technique used in breast screening, per se. It's rather about the practice of mass breast screening of an asymptomatic population. Mammograms can also be used in different situations, for example in women with known symptoms of breast cancer or with a carcinoma discovered through clinical examination. What we say about mass breast screening does not necessarily apply to these other situations.

Like most things, breast screening, i.e. mass mammography, has advantages and disadvantages. Your GP or other doctor, as well as the literature produced and sent out by the government health departments and authorities of many countries, will probably tell you that the benefits outweigh the costs. Let's examine if this is indeed the case.

Breast screening is the mass program of screening, using a technique called mammography.

It is not, as is often believed, a preventive measure. Or we can put it this way: it is not about disease prevention, but mortality prevention. Having the test done does not help to prevent breast cancer. The rationale for it is that, if cancer is detected hopefully in its early stages, the treatment is more likely to be effective and successful than if the tumour has already spread.

For this reason, mass breast screening programs which encourage all women over a certain age (now usually 50) to have regular mammograms, first introduced in Germany in the 1930s, are today in place in many developed countries, albeit with some difference in terms of the age and frequency recommended.

In America, for instance, until 2009 the U.S. Preventive Services Task Force (USPSTF) advised a mammogram every one to two years for all women aged 40 or over, whereas now it considers sufficient a breast screening test every 2 years for women aged 50 to 74. In the UK, the NHS (National Health Service) recommendation is every 3 years for women between 50 and 70.

Breast screening has one clear benefit: if a woman has indeed breast cancer at an early stage which will certainly develop into a malignant tumour, but she has not yet noticed it, and if that carcinoma can be successufully treated, that is either it can be cured or its progression can be halted, the life of that woman can be saved. It is a major achievement, but many 'ifs' must be satisfied first.

On the other hand, breast screening can harm three groups of women.

First, the women who will receive false positives, i.e. will be told that they have cancer when they don't. The damage for these women is both psychological and physical.

Mentally they will have to go through the agony of thinking that they are possibly terminally ill, a shock which should not be underestimated, and from which some women don't fully recover even after they have been informed of the misdiagnosis.

In addition to that, these women will be recalled for further tests, which could involve more mammograms, which most women find uncomfortable and about a third of women painful, and other more invasive exams like biopsies, the removals of breast tissue.

If the erroneous diagnosis continues, these women will be subjected to treatments like lumpectomy (removal of part of the breast), mastectomy (removal of a whole breast), chemotherapy and radiotherapy, all highly invasive forms of treatment with their own side effects, and negatively affecting the quality of life. And all of this for nothing.

The second group of women attending breast screening who will be harmed are those who are diagnosed with Ductal Carcinoma In Situ (DCIS), an early form of breast cancer which has not spread (ergo, it is in situ, Latin for 'in the same place'). When this is discovered, doctors are in a real jam, because it may spread and become malignant or it may never do that: there simply is no way to tell.

The main help for an uncertain prognosis here are the statistics, which say that 1 to 5 cases of DCIS out of 10 will grow into full-blown cancer. When DCIS is discovered, treatment is normally given as if the prognosis were necessarily negative, to be on the safe side.

So those women whose DCIS would not have progressed will suffer all the physical rigours of breast cancer treatment, not to mention all the mental pain, only because breast screening found a carcinoma which would never have given them any problems if they had been left alone.

A similar situation arises when women are so old that, even if a malignant breast cancer is detected, the progression of the disease will be so slow that it will never be felt in their lifetime. This is the reason why for women over 70 breast screening is considered less beneficial, although in the UK for instance the NHS, although its breast screening promotion is targeting only 50-70 year-old women, plans to extend it to women up to 73, and says that women over 70 are always welcome to attend.

The third group of women to pay the cost of mass breast screening are those who were healthy before the mammogram and will get cancer from the test's X rays. This is a tiny proportion.


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Photo accompanying the article Mammogram by National Cancer Institute made available under a Public Domain Mark 1.0.