The claim that cancer screening saves lives is based on the reduction in disease specific mortality. Two doctors and a journalist argue in the British Medical Journal that this is the wrong way of measuring the effect of screenings. According to them, we should use the overall mortality.
The authors write that using disease specific mortality as a proxy for overall mortality fails to inform people about their major concern: reducing the risk of dying. A meta-analysis of ten cancer screening trials showed that three of the studies found a reduction in the disease specific mortality but none found reductions in the overall mortality.
The authors report two reasons for this phenomenon. Many studies may be underpowered to detect a small change in the total mortality and the reductions of the disease specific mortality may be offset by deaths due to downstream effects of screening. These deaths are most likely to occur in screenings with false positive results, overdiagnosis of non-harmful cancers, and detection of incidental findings. As an example they refer to the screening for prostate cancer. These screenings yield many false positive results, forcing patients to undergo a (sometimes harmful) biopsy. In addition, the positive result may trigger heart attacks or suicide attempts or the treatment of a cancer that may never have caused symptoms might increase the disease specific mortality.
The authors have several pieces of advice for the future. Trials should be ten times larger and powered for the detection of changes in overall mortality. To reduce costs, the first trials could just target the highest risk groups. The authors also call for higher standards of evidence for cancer screening and encourage healthcare providers to be honest about the limitations of screening, because ‘the harms of screening are certain, but the benefits in overall mortality are not.’
Want to know more about this subject? This infographic explains the importance of reporting all causes of mortality in cancer screening trials.
Source: British Medical Journal