Mammography is a procedure in which the breast is examined using a special X-ray machine to detect signs of cancer. The rationale is that early detection enables treatment to be started before symptoms become evident thereby increasing the chances of curing or controlling the disease. This approach is utilised in many countries and in the UK is being actively promoted by the NHS.
As long ago as 1978 the Office of Technology Assessment (OTA) in the USA reported that questions were being raised about the safety of the procedure (1). In a report the OTA noted that many in the medical profession believed that it was efficacious and safe for all women, but there is no scientific information derived through controlled studies to support such a view. It was concluded that the technology had been introduced on an extensive scale before doubts about its safety raised questions about its effectiveness.
These fears were confirmed by the results of a study based on data collected in the Norwegian Breast Cancer Screening Program. The incidence of breast cancer in one group consisting of 119,472 women aged 50-69 at the outset who were screened using mammography on 3 separate occasions was assessed. This was then compared with the results for a similar control group of 109,784 women who were only screened on one occasion which was at the end of the 6-year period. It was found that the cancer incidence in those who had been screened 3 times was 22% higher than in those who were screened once. As expected the incidence of breast cancer was considerably higher in those who were screened at the beginning of the 6-year period because many cancers were only detected due to the screening. The authors were surprised to find that there was still a higher incidence in the group which had multiple screenings at the end of the period. If the screenings were performing as expected then this group should have had less cancer because the rationale is that the detection should enable the cancer to be treated. The explanation suggested was that many cases of breast cancer recover spontaneously. This means that the treatment for these particular cases is totally unnecessary and may actually be counter-productive (2).
A more recent evaluation was conducted by the Nordic Cochrane Collaboration which concluded that if 2000 women are regularly screened for 10 years one will benefit from the screening, as she will avoid dying from breast cancer. At the same time, 10 healthy women will, as a consequence, become cancer patients and will be treated unnecessarily. These women will have either a part of their breast or the whole breast removed, and they will often receive radiotherapy, and sometimes chemotherapy. These numbers were derived from the randomised trials of mammography screening. However, since the trials were performed, treatment of breast cancer has improved considerably. More recent studies suggest that mammography screening may no longer be effective in reducing the risk of dying from breast cancer. Screening produces patients with breast cancer from among healthy women who would never have developed symptoms of breast cancer. Treatment of these healthy women increases their risk of dying, e.g. from heart disease and cancer. It therefore no longer seems beneficial to attend for breast cancer screening. In fact, by avoiding going to screening, a woman will lower her risk of getting a breast cancer diagnosis (3).
Nevertheless here in the UK the NHS continues to claim that mammography screening will save 1400 lives per year. However a paper by Peter C Gøtzsche and Karsten Juhl Jørgensen of the Nordic Cochrane Centre published in the Journal of the Royal Society of Medicine entitled “The Breast Screening Programme and Misinforming the Public” challenges this position (4). They argue that the harm has been “downplayed” and that the information provided for the public has remained largely unaffected by “repeated criticism and pivotal research” which has questioned the benefits of screening and documented substantial over-diagnosis.
The paper states that information regarding lives saved through the screening programme is much exaggerated. “The claim that death rates have fallen ‘in part from earlier diagnosis associated with screening’ is astonishingly misleading,” says Peter Gøtzsche, who is the Director of the Nordic Cochrane Centre. “Deaths from breast cancer are falling because treatment is improving. There’s been a similar fall in the age-groups not invited to screening. In this respect, and many others, the Programme persists in misinforming the public. It was forced to revise its leaflet inviting women for mammography but the new leaflet and their latest Annual Review continue to repeat incorrect mortality estimates.”
According to the NHS Programme, screening will prevent one death from breast cancer for every 400 women screened regularly over ten years. Gøtzsche and Jørgensen were unable to find any evidence for this estimate in reports from the Programme or elsewhere. Based on studies in Sweden a more realistic estimate would be one death prevented for every 2000 women screened, which means the NHS figure is 5 times too high.
The authors also point out that the NHS publicity is ambiguous with respect to the over-diagnosis, which means that those considering screening do not appreciate the risks involved. Information from Denmark shows that the incidence of mastectomies is increased substantially as a direct result of over-diagnosis. However the impression presented by the NHS is that screening will reduce the chances of a woman requiring a mastectomy and is therefore seriously misleading.
This is another example of how the hierarchy in the medical profession persists in pushing a strategy which quite simply flies in the face of the latest evidence. The fact that more and more people can do their own investigations using the internet will ultimately undermine the official policy. In the meantime many people will suffer unnecessarily and public money will be wasted on a procedure that is clearly “not fit for purpose”.
Further insight into this topic can be found on the Canceractive website (5).
- P-H Zahl et al (2008) JAMA Internal Medicine 168 (21) pp 2311-2316