Does Mammography Help?

phpWE6P9ePMMammography, in its hunt to irradiate every woman’s breasts and find ever more cancers, started a slash and burn war that the work of Danish researcher, Peter C.Gøtzsche, should have ended a decade ago.


Gøtzsche’s work shows that there is absolutely no evidence that mammography has decreased the overall death rate from cancer. While some studies (that he considers biased) show a reduced death rate from breast cancer, he shows that they also show an increased overall death rate—which is clearly more important.

The failure of the war can be summed up in the frequently repeated, and apparently positive, statement that the death rate among women with breast cancer has declined as mammography has expanded. This lie with a thin veneer of truth indicates how the profitable industry uses statistics to mislead and just how difficult it can be for a woman to decide for herself whether to have a mammogram when faced with conflicting statistics.

Gøtzsche has done the world a favor by painstakingly showing why this apparent success is actually a dramatic indication of the failure of mammography, starting with his first statistical analyses in 1999 and now his 2012 book, Mammography Screening: Truth, Lies and Consequences, which summarizes all his work in a more accessible format than the scientific articles scattered over a number of years and a number of journals.


The statistic that the death rate among women with breast cancer has declined is dramatically misleading because the overall death rate from breast cancer has not. The death rate among women with breast cancer is the number of deaths in these women divided by the number of cases. The easiest way to reduce the statistic is to increase the number of cases of breast cancer, and Gøtzsche shows that is exactly what mammography does.

A chapter in his book entitled “Overdiagnosis and Overtreatment” uses graphs from a number of studies to show dramatic increases in breast cancer diagnosis after the introduction of screening programs—in Copenhagen (where screening took place) but not in the rest of Denmark (where there were no screening programs at the time), as well as among women in the age groups being screened in New South Wales (compared to pre-screening statistics).


Before mammography, women were diagnosed with breast cancer when they had a noticeable tumor. It seemed like a perfect plan to diagnose women when their tumors were at an earlier stage when treatment would be easier, less disfiguring and more likely to be successful.

If you go back far enough, however, in the life of a deadly cancer, looking for smaller and smaller tumors, it becomes impossible to distinguish between the tumor that will metastasize from the one that is growing so slowly it will never cause a problem in a woman’s lifetime or to distinguish the one that is not growing at all from the one that will later regress and disappear.


One of Gøtzsche’s most fascinating sections is on the evidence that a significant percentage of small breast tumors can regress, a fact that is largely unknown. He cites a Journal of the National Cancer Institute paper estimating that an incredible 40% of detected breast cancers would regress if left alone.

He also demystifies the term “in situ” (e.g. in-situ ductal carcinoma). This refers to a cancer that is not growing, which means—by the understanding of the average woman— that this is not a cancer at all. Yet, if found, the tumor will generally be treated.

Through an anlysis of five studies, Gøtzsche’s  shows that mammography results in about 50% more cancers, a conclusion supported by independent research. Over-diagnosis of insignificant tumors means that women will be more likely to survive five or ten years after their diagnosis.


Gøtzsche is very critical of this as a measure of  ‘cure’ because of two biases. The first is that if dangerous tumors are detected earlier in many women, but treatment is not actually beneficial, the five or ten year survival rate will increase.

The second problem with the use of five or ten year survival as a measure of success is that if there is an over-diagnosis of tumors that are not dangerous at all (and the lack of improvement in the overall death rate shows that this is the case), the results will improve as more healthy women live past five or 10 years, women who would have lived even longer if never diagnosed.

Statistics vary from study to study, but if the number of treatments (e.g. mastectomy and lumpectomy) incease by 30%, almost half of women will experience at least one false positive out of ten mammograms and almost 20% will endure an unnecessary biopsy.[Elmore, 1998]


A big problem with mammography is that it is not even good at finding serious, fast-growing cancers. If screening is annual, fast growing cancers may easily be undetectable one year and a serious problem before the next screening. Slow growing or non-growing cancers are much easier to find because they will be there for many screening sessions. Screening more frequently could help, but screening twice a year would increase the harms of mammography as well.


Mammography, like so many other forms of screening, has become widely accepted because it is heavily promoted, not because it has been shown to work. It is heavily promoted because it is highly profitable, not so much from the screening as from the many unnecessary medical procedures it generates. The antidote is information and luckily it is not difficult to find with a little bit of work. If the more than 350 pages in Gotzsche’s Mammography: Screening, Truth, Lies and Controversy is too much, you can review his free pamphlet on screening, available in English and several other languages, with references.


David CroweDavid Crowe is a medical science critic, environmentalist, writer and activist. He is co-founder and co-host of the podcast, “How Positive Are You?” David has been President of Rethinking AIDS since 2008, and was one of the founders of the Green Party of Alberta. He has written for numerous magazines on health and technology topics, and has peer-reviewed articles in biology and computer science. He graduated with a degree in biology and mathematics but has worked in the fields of computer software and telecommunications.

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