NEW YORK (Reuters Health) – A review of the literature has shown that the most important harms from cancer screening are often not quantified in screening trials.

“Healthcare decision makers, healthcare practitioners, and, ultimately, patients therefore cannot make informed choices about cancer screening. This is problematic as many cancer screening programmes have important associated harms,” the Danish investigators comment in their paper in the British Medical Journal published online September 16.

As they point out, cancer screening can lead not only to benefit but also to harm, such as from investigations of false positive findings, overdiagnosis and overtreatment, and adverse psychosocial consequences.

“Screening should be offered only when the benefits are firmly documented and considered to outweigh the harms, which should be equally well quantified,” they write.  However, there is evidence that cancer screening trials do not consistently quantify associated harms.

To investigate further, Dr. Bruno Heleno, at the University of Copenhagen, and colleagues identified 57 randomized trials that assessed the efficacy of screening for reducing cancer incidence and mortality.

They found the two most important harms – false positive findings and overdiagnosis – were quantified in only two (2%) and four (7%) of the trials, respectively.

Other potential harms and the proportion of trials in which they were quantified included negative psychosocial effects (9% of trials), somatic complications (19%), invasive follow-up procedures (47%), and withdrawal because of adverse effects (2%).

In fact, the authors report, the median amount of space in the studies allocated to reporting harms was 12% of the results section.

“If trialists do not report certain outcomes because they consider that the harms will be either rare or irrelevant when compared with the potential decrease in mortality, such information will not be available for people who judge these outcomes differently,” Dr. Heleno and colleagues argue.

They say future screening trials should collect and report data on harms of screening.  Furthermore, they add, “Adequate reporting of harm requires data from the control group as these provide a reference level and help to interpret harms data from the screened group.”

SOURCE: Quantification of harms in cancer screening trials: literature review
Br Med J 2013.