De wetenschappelijke basis van het bevolkingsonderzoek naar borstkanker in Nederland

- A recent Cochrane review stated that there was a lack of evidence for a decrease in mortality as a result of population breast-cancer screening. The principal data were drawn from five Swedish randomized controlled trials and one Canadian trial.

- However, the studies cannot be so easily combined because there were important differences in the attendance rate, detection rate, technical quality, referral rate, clinical baseline situation and screening interval.

- For example, in one of the studies the women from the control arm underwent an annual clinical palpation carried out by a trained nurse or physician, which could have led to an underestimation of the screening effect.

- Further breast-cancer mortality might not be a good outcome measure because this was not reliably determined; only total mortality was to be observed. This is clinically and methodologically incorrect because breast-cancer mortality was meticulously studied, documented and validated.

- In the Cochrane review it is suggested that the randomisation was inadequate, but evidence for this was not supplied. The discussion about age differences as a marker for incorrect randomisation is out of date and has been revealed to be unjust.

- It seems likely that an important part of the decreasing trend in breast-cancer mortality in several countries (including the Netherlands) is due to screening programmes. However, the evaluation of breast-cancer mortality over the next five years is crucial, if greater certainty is to be gained about this.