Many years ago (more than I care to remember), I was giving a lecture about health, and more in passing that anything else, mentioned just how ineffective many conventional medical approaches are, including cancer screening. After the lecture I was approached by a woman who took at least some exception to my claim that cancer screening was not very effective. She told me that if it were not for mammography, she would be dead. In short, ‘mammography saved her life’.
When she put it this to me I enquired gently why she felt she could state that with such certainty, and she replied that breast cancer is a killer and that it was only because it was caught early that she did not succumb to it. Besides, her surgeon had told her early detection had saved her life.
I wasn’t intimate with her medical history, but the fact is her firm belief that mammography saved her life is probably just that – a belief. While it’s natural perhaps to imagine that every time mammography picks up cancer that is successfully treated that has saved the sufferers’s life, the fact is this is far from assured.
One reason why mammography may not save lives even when it detects cancer is because breast cancer treatment is actually relatively effective (as cancers go). So, imagine this lady had not had screening and the cancer had been detected clinically (say she or her doctor noticed a breast lump), it is entirely possible that her breast cancer could have been cured despite being detected later. In this case mammography would have not saved her life – it would have just afforded her earlier treatment.
Another very real possibility is that the cancer this woman had would never have bothered her over the natural course of her life anyway – a situation referred to as ‘over-diagnosis’. In which case, again, her life would not have been saved by mammography, but she would have undergone unnecessary treatment which is not without risk, either.
I was very interested to read a recently published paper in which researchers calculated the likelihood that mammography which detects breast cancers that are successfully treated actually saves lives [1].
The researchers made this calculation based on women of different ages, and the different estimates for the ability of mammography to reduce breast cancer death. The very best estimates from old and outdated evidence suggest a reduction in death risk from breast cancer of 25 per cent. However, as the authors point out, never, better evidence suggests that the likely real reduction is risk is between 5 and 10 per cent.
Using a 50-year-old woman as an example, the authors tell us that if mammography reduces risk of breast cancer death by 20 per cent, if mammography detects a cancer which is successfully treated, the chances that this has saved her life are just 13 per cent.
If mammography were to only reduce the risk of breast cancer death by 5 per cent (much more realistic), the chances that mammography had saved this woman’s life are a measly 3 per cent.
In other words, the vast majority of women who have mammography and go on to have successful breast cancer treatment have not had their lives saved at all. This is not a reason not to have mammography. However, it is perhaps worth bearing these facts in mind when we read about or hear of the ‘success stories’ women who have undergone mammography and subsequent successful treatment for cancer. Only a small minority of these women have had their lives saved, despite how it looks and how their stories are often presented.
References:
1. Welch HG, et al. Likelihood that a woman with screen-detected breast cancer had had her “life saved” by that screening. Archives of Internal Medicine. Epub 24th October 2011
