Storm in a C cup
Written by David Fisher
When car mechanics perform MOTs, it is quite common for them to alert drivers when they dis- cover damaged car parts. For example, they may issue a warning that the brakes may fail unless the pads are replaced. This is not to say that every driver who ignores such advice will experience a crash. Even if the majority of people with worn out brake pads did not experience crashes it would be absurd to say that MOTs are unnecessary. A similar argument has arisen with breast cancer screening. The detection and overtreatment of ductal carcinoma in situ, an early form of cancer that may not progress to invasive carcinoma, has led some to leap to the conclusion that the entire breast screening process should be questioned.
The evidence supporting breast cancer screening is strong. The World Health Organisation claims breast screening reduces mortality by 35%. The National Health Service (NHS) maintains 1400 lives are saved each year because of breast screening but recently this figure has been disputed. A paper published in the British Medical Journal puts forward the theory that reduction in breast cancer mortality has been due to improvements in treatments rather than screening. The robustness of the pro-screening evidence has been called into question amid suggestions the health service has been floating a lame duck all along.
A related issue has also been brought to the surface in the recent storm of articles questioning screening. The objective of screening women aged between 50 and 70 is to detect carcinoma growths that would otherwise have not been detected and become harder to treat as the cancer progressed. The test is sensitive and is capable of finding small benign growths, ductal carcinoma in situ, less than half of which progress to a more dangerous form. An independent estimate predicts that for every 2,000 women screened, only one life is saved who would otherwise have died. This is compared with the NHS claim of five lives being saved. A further ten women are treated unnecessarily for ductal carcinoma in situ, contrary to the two predicted by the NHS, and an additional 200 women receive false positive results that are mostly dismissed following biopsy. On the face of it, these pessimistic figures make screening appear helpful in a few cases and harmful in a great number more. However, if these statistics are assumed to be accurate and applied to a one million women screening population, 500 lives would be saved. Surely this is quite a significant number, sufficient to continue recommending screening. The confounding issue would be the 5000 women unnecessarily treated but this is a separate problem that can be remedied. What has really irritated researchers is that the public are not fully informed about the dangers of radiotherapy and mastectomies that may be used to unnecessarily treat harmless lesions.
Essentially, there are three separate issues which are being mingled in the media hype but must be addressed individually.
First, the question must be answered whether breast cancer screening results in reduced mortality. To suggest mortality has reduced but has done so because of improved treatment completely independently of early diagnosis from screening flies in the face of accepted dogma and is contrary to the conclusions from a heap of data that form the basis for screening. Conventional wisdom states logically that early diagnosis of conditions leads to better treatments.
Second, are we responding correctly to the results of screening? The key statistic that has sprouted so much negativity is the number of women subject to unnecessary treatment of ductal carcinoma in situ. When these lesions are detected it is impossible to determine whether they will become malignant or not. A knee-jerk reaction encouraging treatment of every possible carcinoma has likely developed from fear of being sued for negligence after dismissing lesions that subsequently become invasive. Management of these cases seems to gravitate towards intervention on the basis of ‘rather safe than sorry’. Rebalancing the scales in favour of frequent monitoring of unclear cases would help weed out overtreatment of tumours that remain in the benign state.
Finally, the patient information leaflet is wholly inadequate. Mike Richards, a national director for the Department of Health has already announced a second revision of the leaflet. No doubt it will be rewritten to include more comprehensive information about different diagnoses and the respective prognostic likelihoods which will enable more informed treatment decisions to be made.
The current controversy needs to be calmed for fear patients will no longer believe screening is beneficial. The newly formed independent review must swiftly pour oil on the troubled waters that have been so violently stirred.
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