An independent investigation into breast cancer screening has been set up by the government’s cancer chief to try to settle the growing controversy around its usefulness and potential harms.Prof Sir Mike Richards‘s move is an attempt to put to rest the criticisms of a number of scientists, who say the NHS (British National Health Service) screening programme wrongly identifies cancers that might never harm women, leading to unnecessary and potentially damaging treatment with surgery, drugs and radiation therapy.They also contest the official NHS position, which is that although there is some over-treatment as a result of screening, mammograms save lives.
“I declined screening when it was offered, as the NHS breast screening programme was not telling the whole truth. As a non-expert in the subject, I found myself examining the evidence for breast screening with increasing doubts. I compared the NHS and Nordic Cochrane Centre leaflets and found that the NHS leaflets exaggerated benefits and did not spell out the risks. Journals showed a reputable and growing body of international opinion acknowledging that breast cancer screening was not as good as used to be thought. The distress of overdiagnosis and decision making when finding lesions that might (or might not) be cancer that might (or might not) require mutilating surgery is increasingly being exposed. The oft repeated statement that “1400 lives a year are saved” has not been subjected to proper scrutiny. Even cancer charities use lower estimates. I expressed my misgivings to you “behind the scenes” as a work colleague. You replied in a personal email “that the large majority of experts in this country disagrees with the methodology used in the Cochrane Centre reviews of breast screening.”It is extraordinary to be told that methodology is contentious so many years into the national programme.”
“I take the current controversy very seriously. I will do my best to achieve consensus on the evidence, though I realise this may not ultimately be possible. Should the independent review conclude that the balance of harms outweighs the benefits of breast screening, I will have no hesitation in referring the findings to the UK National Screening Committee and then ministers. You also have my assurance that I am fully committed to the public being given information in a format that they find acceptable and understandable and that enables them to make truly informed choices.”
Background Perhaps the most persuasive messages promoting screening mammography come from women who argue that the test “saved my life.” Because other possibilities exist, we sought to determine how often lives were actually saved by mammography screening.Methods We created a simple method to estimate the probability that a woman with screen-detected breast cancer has had her life saved because of screening. We used DevCan, the National Cancer Institute‘s software for analyzing Surveillance Epidemiology and End Results (SEER) data, to estimate the 10-year risk of diagnosis and the 20-year risk of death–a time horizon long enough to capture the downstream benefits of screening. Using a range of estimates on the ability of screening mammography to reduce breast cancer mortality (relative risk reduction [RRR], 5%-25%), we estimated the risk of dying from breast cancer in the presence and absence of mammography in women of various ages (ages 40, 50, 60, and 70 years).Results We found that for a 50-year-old woman, the estimated risk of having a screen-detected breast cancer in the next 10 years is 1910 per 100 000. Her observed 20-year risk of breast cancer death is 990 per 100 000. Assuming that mammography has already reduced this risk by 20%, the risk of death in the absence of screening would be 1240 per 100 000, which suggests that the mortality benefit accrued to 250 per 100 000. Thus, the probability that a woman with screen-detected breast cancer avoids a breast cancer death because of mammography is 13% (250/1910). This number falls to 3% if screening mammography reduces breast cancer mortality by 5%. Similar analyses of women of different ages all yield probability estimates below 25%.Conclusions Most women with screen-detected breast cancer have not had their life saved by screening. They are instead either diagnosed early (with no effect on their mortality) or overdiagnosed.
by Carlos Fernández Oropesa
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