A few weeks ago I attended the European Society of Medical Oncology conference in Milano.
One of the sessions was dedicated to the pros and cons of breast cancer screening. Karsten Jørgensen, of the Nordic Cochrane Center in Copenhagen, played devil’s advocate and discussed the perils derived by over-diagnosis of breast cancer due to mammography.
There are some famous precedents where over-diagnosis led to abandonment of the screening programmes: lung cancer with chest x-ray was dropped as a screeening programme when 29-50 % more cases were found in the screened group. The same happened with prostate cancer screening with PSA (20-70 % extra cases in screened group) and screening for neuroblastoma in children with urine test: 100 % over-diagnosis in two independent trials. Not to talk about the final screening test: autopsy, where practically every single one of us is found to have thyroid lesions!
Two fundamental concepts need to be spelled out and properly defined for every screening programme that we undertake:
1) Over-diagnosis, defined as the phenomenon for which, if screening were detecting breast cancer that would otherwise not have been diagnosed, it would be expected that in controlled trials there would be a persistent excess number of breast cancers in the screened group compared with the control group (the definition is taken from the 1986 Forrest Report, which formed the basis for the breast cancer screening programme in the UK).
2) Over-treatment: an obvious source of harm associated with any screening programme is unnecessary treatment of cancers that were not going to cause death or symptoms (from the 2003 IARC Handbooks of Cancer Prevention)
The problem is not so much the former, as the latter: not overdiagnosis, but overtreatment. Just think how you would explain to a woman that the surgery, radiotherapy or chemotherapy she underwent, together with all the worries and preoccupation that she and her family went through, were unnecessary…
The Nordic Cochrane Center (NCC), where Jorgensen works, is an independent research and information centre that is part of the Cochrane Collaboration (an international network of individuals and institutions committed to preparing and disseminating systematic reviews of the effects of health care). A review about breast cancer screening with mammography was compiled in 2009, and is available upon downloaded on their website: http://www.cochrane.dk/.
To put the results of the review in simple but telling figures, for every 2000 women invited for screening throughout ten years, while one will have her life prolonged, ten other healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than two hundred women will go through psychological distress due to false positive results.
Therefore, it is thus not clear at all whether screening does more good than harm. Jørgensen is inclined to think that it does not, and he concluded his talk with another thought-provoking message with which I also want to leave you. He showed an old print campaign advertisement by the American Cancer Society, which reads: “If you haven’t had a mammogram, you need more than your breasts examined”.
But, given the current Cochrane data, is it still true that women would behave stupidly, if they decided not to undergo mammography screening?