Commentary: a defence of the Health Insurance Plan (HIP) study and the Canadian National Breast Screening Study (CNBSS).

Gotszche and Olsen2,3 focuses largely on three of the screening trials, and they conclude, like the International Agency for Research on Cancer (IARC) working group that reviewed all the trials,4 that mammography screening does save lives. I agree with their comments on the Health Insurance Plan (HIP) trial. I drew very similar conclusions when the first review of Gotszche and Olsen was published.5 Having been a participant in the IARC working group that reached similar conclusions to Freedman et al. on the Two County trial, and having found the analysis of Nixon et al.6 particularly compelling in largely dealing with the cluster randomization issue, I also agree with most of their comments on that trial, though I still have some caveats on its application at the present time. However, Freedman et al. cite the analysis of Nystrom et al.7 as demonstrating equivalence in breast cancer incidence prior to randomization. They neglect to mention that Nystrom et al.7 were only able to assess this in regard to Ostergotlund, as Tabar declined to produce the data for the Kopparberg component of the trial for this overview analysis. Thus we still do not have absolute certainty that the clusters in Kopparberg were balanced. More important, it is not clear that either the HIP or the Two County trials are relevant to the present time, when women with stage 2 breast cancer invariably receive adjuvant chemotherapy or hormone therapy, not available at the time of HIP, and apparently not given in the Two Counties in Sweden when that trial was conducted.8,9 The availability of such therapy IJE vol.33 no.1 © International Epidemiological Association 2004; all rights reserved. International Journal of Epidemiology 2004;33:64–65 DOI: 10.1093/ije/dyh015