Asking the obvious
March 1st 2010, 17:41
Someone finally bothered to ask the question: does breast screening work? The answer is a damning and resounding no, as our cover story this month makes clear. No breast screening programme anywhere is making the slightest impact on cancer mortality.
According to the prestigious Cochrane Collaboration, which carried out one of the most extensive and unbiased reviews of the literature to date, mammograms not only don't work as a screening tool, but also increase your risk of cancer and unnecessary treatment.
In fact, because of its high likelihood for false-positive readings and for highlighting benign abnormalities, screening may only be increasing the number of patients mutilated through uncalled-for drug treatment or surgery.
Breast cancer screening of the young and healthy largely began in the early 1990s, when a Swedish review concluded that regularly screening reduced mortality by 30 per cent in women aged 50 and over. Yet, in spite of the proviso that this did not apply to women younger than 50, the '30-per-cent risk reduction' was adopted as a mantra by the medical profession to justify screening a number of population groups, including younger women.
And despite all the medical evidence to the contrary, doctors urged all women-even those as young as 30-to have annual mammograms.
However, on examining the Swedish statistics, you'll see a little statistical quickstep: the 30-per-cent improved survival rate is derived from looking at the "most scientific" screening studies and pooling the results. The studies were of two types: those that looked to see what happened over time in various groups of women; and those that retrospectively analyzed what had already happened in groups of women.
Most of the studies on their own showed no clear benefit. Of four such trials, three showed no statistically significant benefit-not even in women aged 50 and over. Two of these studies involved 80,000 women, yet were dismissed as "too small" by screening proponents.
Since then, there has been little evidence that mammography benefits anyone in any age group, but lots that it does great harm through false-positives and get-in-there-early interventions. One review found that only one in 14 women with a positive mammogram result for breast cancer will, in actuality, have the disease.
A major problem of modern medicine is what I call 'medicine by conventional wisdom', based on the assumption of a priori benefit. The idea of spotting cancer as early as possible was such an obviously good idea that, for years, no one thought to question it, much less study it.
Yet the concept, of course, assumes that the technology is perfect, whereas mammograms-which are only suped-up X-rays of soft tissue- are far from being either accurate or benign. The problem is that they reveal a raft of insignificant variants of breast tissue, and then manage to miss the elephant in the room-the malignant tumour. The other problem is that the X-rays themselves, used regularly, cause cancer.
Thankfully, this time the Cochrane scientists finally asked the obvious question-does it work?-that no one else had dared to.