A massive new study has concluded that getting regular mammograms – which women have been urged to do for decades – does not reduce the risk of dying of breast cancer.
It is sobering news, and creates a good deal of confusion.
But, practically, should women behave differently as a result of this news?
The short answer is: Not especially.
In the coming days, weeks and months, there will be a fierce dogmatic debate, with one camp arguing screening is essential and life-saving, and the other saying mammography screening does more harm than good. And it will quickly degenerate into a technical debate about methodology and whose data are better.
The truth, as is often the case, lies somewhere in the middle.
Mammography has its place – especially as a diagnostic tool. But mass screening also has some significant shortcomings that should make us question its value.
Let's review the findings of the Canadian National Breast Screening Study. The research involved 89,835 women aged 40 to 59. All underwent an annual physical breast exam, while half were randomly assigned to undergo annual mammograms for five years, beginning in 1980.
By 2005, 3,250 of the 44,925 women in the mammography arm of the study were diagnosed with breast cancer, and 500 had died of it. The control group of 44,910 women had 3,133 breast cancer diagnoses and 505 breast cancer deaths.
In short, it was a wash.
Is that because mammography is of no benefit? Is it because treatment has improved? Many factors can help explain breast-cancer mortality.
But evidence has been building that the premise on which mass screening programs rest – that the earlier cancer is discovered, the less likely it is to be fatal – is not necessarily correct.
For the most part, breast cancer develops slowly. When women are screened, there are four possible outcomes:
- No cancer is found, which is the case with most mammograms.
- An aggressive cancer is detected. These women would have died had they not been screened and they will still die. Most breast cancer deaths fall into this category.
- A potentially lethal cancer is detected before it can spread, and death is averted. Research (but not the new study) places 10 to 30 per cent of cancers in this category, depending on age.
- Detection of breast cancers that will never be fatal because the patient dies of something else first; the result is often over-treatment, meaning unnecessary surgery, radiation or chemotherapy.
The real frustration is that we have little idea who can benefit most from screening. There are now targeted screening programs for women with the so-called breast cancer genes BRCA1 and BRCA2, but no way of knowing which ones will benefit from early detection. In trying to find those cases, many women may be treated unnecessarily, about one in every 424 who are screened according to the new research. With millions screened annually, that's a lot of collateral damage.
The response to these challenges in recent years has been to dial back the push for screening. For a long time, annual mammograms were recommended, and some advocated starting at age 40. But now the Canadian Task Force on Preventive Health Care advises women to have mammograms every two to three years between the ages of 50 and 74.
That is the sensible way to go.
Women should continue to be screened – because the jury is still out on the benefits – but do so every few years without stressing about it. They should also be as aware of the possible harms as the potential benefits.
We should also not get caught up in the screening debate to the exclusion of everything else.
Breast cancer will kill an estimated 5,000 women (and 60 men) this year. That number has been falling steadily, and represents about four per cent of all women's deaths. Fear should not hang over women like a dark cloud.
Mammography is not going to save women magically from breast cancer; the best protection will come not from screening but a healthy lifestyle – not smoking, limiting alcohol consumption, maintaining a nutritious diet and being physically active.