Last week one of my blogs focused on prostate cancer screening, and specifically the prostatic specific antigen (‘PSA’) test. For a variety of reasons, the doctor who discovered PSA says the practice of using it to detect cancer should be stopped. In that post, I mentioned that doubts have also previously been raised about the usefulness of mammography. Just a few days later, as it happens, the British Medical Journal published a paper which asks serious questions about the relevance of this practice.
The study in question focuses on breast cancer screening in Denmark. Mammography has previously been said to reduce risk of dying from breast cancer in Denmark by 25 per cent. However, as the authors of this recent study point out, just because breast cancer mortality fell after the introduction of mammography, does not mean that mammography is responsible. The reduction in mortality might be due to other factors, such as changes in risk factors or improvements in treatment.
To get a more accurate picture reading the effectiveness of mammography, the researchers compared changes in breast cancer deaths in regions where mammography had been introduced, and compared this with death rates in regions where mammography had not been introduced. Here’s what they found:
Over a 10-year period where screening could have saved lives, in women of an age who might benefit from screening (women aged 55-74), death rates from breast cancer fell by 1 per cent per year. This decline was not statistically significant.
In comparison, death rates in non-screened areas fell by 2 per cent per year over the same time period. And this fall was statistically significant.
The authors of this study also compared these findings with death rates in women too young to have benefitted from mammography. In the screened area, death rates fell by 5 per cent per year. In the non-screened areas, death rates fell by even more, though (6 per cent year).
The authors point out that their findings are not new, and in fact are in line with findings from other parts of the World. For example, they note:
“In the UK, where screening started in 1988, the decline in breast cancer mortality from 1989 until 2007 was 41% in women aged 40-49 years, who were not invited to screening, 41% in women aged 50-64 years, who were invited to screening from 1988, and 38% in women aged 65-69 years, who were invited from 2002. Furthermore, the drop in breast cancer mortality in the relevant age group began before the screening programme started, and was largest in the age group that was too young to be invited (40-49 years) if the whole observation period is considered (1971-2007).”
They also draw our attention to a European study that found that falls in breast cancer mortality in countries offering and not offering screening were of a similar size. The greatest declines were seen in women who were too young to be offered screening, which points to factors other than screening (such as improvements in treatment) as the real reason for declining breast cancer death rates.
Here are the conclusions from the BMJ study:
“We were unable to find an effect of the Danish screening programme on breast cancer mortality. The reductions in breast cancer mortality we observed in screened regions were similar or larger in non-screened regions and in age groups younger than that screened. The mortality reduction is therefore more likely to be explained by changes in risk factors and by improved treatment than by screening mammography. Our results are similar to what has been observed in other countries with nationally organised programmes. We believe it is time to question whether screening has delivered the promised effect on breast cancer mortality.”
Mammography on the outside appears so obviously the right thing to do to many. As a result, it perhaps has not been subjected to as much scrutiny as it should have been. It seems to me that there is at least some evidence which seriously calls into question the usefulness and appropriate of this practice. See here and here for more on this.
Mammography is, in my view, a highly politicised practice, and as with such things, there are always going to be individuals on both sides of the debate. For a long time it’s been ardent supporters of mammography that have largely had the floor. What is gratifying, I think, is that more and more the other side of the story is getting an airing. It is because of this that women may, eventually, be in a position to make a truly informed decision about whether to have a mammogram or not.
References:
1. Jorgensen KJ, et al. Breast cancer mortality in organised mammography screening in Denmark: comparative study Per-Henrik Zahl, Peter C Gotzsche BMJ 2010;340:c1241
2. Levi F, et al. Monitoring the decrease in breast cancer mortality in Europe. Eur J Cancer Prev 2005;14:497-502
