- The best evidence that we have about the effectiveness and harms of breast screening comes from a large review done independent of the breast screening industry – with a patient information booklet available here – which states that
- It may be reasonable to attend for breast cancer screening with mammography, but it may also be reasonable not to attend because screening has both benefits and harms
- If 2000 women are screened regularly 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
- Furthermore, about 200 healthy women will experience a false alarm. The psychological strain until one knows whether it was cancer, and even afterwards, can be severe
So. The new leaflet intended for women being given breast screening appointments had been hoped to address the disparity in information. The fact that there was to be an updated leaflet was was announced shortly after this letter had been published in the Times in 2009.
I don’t like the new leaflet. I have tried to see past the pink flowers on the front, which annoy me before I get to the text.
The benefits of breast cancer screening are listed as
-the earlier breast cancer is found the better your chance of surviving it
-if breast cancer is found early you are less likely to have a mastectomy or chemotherapy.
The downsides are listed – in order – as xray exposure, false negatives, false positives, the finding of non harmful ‘cancers’ and anxiety.
In some ways this is a slight improvement. Radiation wasn’t mentioned directly as a harm in the previous equivalent leaflet.
And it does mention DCIS (ductal carcinoma in situ) as a cause of a quarter of screening cancer diagnoses (although I think their wording could be clearer.) Critically, though, they say that they use ‘treatment’ for all DCIS but they don’t make clear that a minority of DCIS go on to invasive cancer, often over decades, and what that treatment is – it is often mastectomy.
But the biggest problem is the numbers they give right at the end. They say that ‘for every 400 women screened regularly for 10 years, one less will die from breast cancer.’
This figure is troubling. It is not based on the best available data, and the source for these figures has never been made clear to me, but here’s the trail.
The original reference is here, in the Journal of Medical Screening from 2006 in a paper written by the Advisory Committee on Breast Cancer Screening:
“The International Agency for Research on Cancer (IARC) concluded that the 25% reduction in mortality seen in the trials of mammographic screening, based on an ‘intention to treat’ analysis, implies a reduction in breast cancer mortality of about 35% for women who are screened regularly. The effectiveness of screening in the NHSBSP is inﬂuenced by programme factors, such as the introduction of two views and the optimization of optical density, and also by population factors, such as the increasing use of hormone replacement therapy during the 1990s. The current NHSBSP saves an estimated 1400 lives each year in England.”
And that’s it. Note the word ‘estimated’.
As for the IARC, here’s the info from the WHO website, from 2002.
“The available evidence on breast cancer screening was evaluated in Lyon by a Working Group convened by the International Agency for Research on Cancer (IARC) of the World Health Organisation (WHO), from 5-12 March 2002. The group, consisting of 24 experts from 11 countries, concluded that trials have provided sufficient evidence for the efficacy of mammography screening of women between 50 and 69 years. The reduction in mortality from breast cancer among women who chose to participate in screening programmes was estimated to be about 35%.”
Yes, it’s ESTIMATED again.
Compare that to the work of the Nordic Cochrane Centre who actually got the studies and looked for the evidence: see here.
And at the end, there’s more of those pink flowers. I may yet weep.