Long-term follow-up in cancer prevention trials (It ain't over 'til it's over)

The update of the Study of Tamoxifen and Raloxifene by Vogel et al. (beginning on p. 696 in this issue of the journal) highlights the overall importance of long-term follow-up of cancer prevention trials, which need long follow-up to fully determine agent risks and benefits. Biomarkers (e.g., reduced cervical intraepithelial neoplasia 3 after human papillomavirus vaccination) can provide an early indication of efficacy but almost never replace the cancer end point in determining the ultimate utility of an agent. Long follow-up is also important to fully determine preventive benefit, as illustrated by the tamoxifen trials, where only 60% as many treated women were needed to prevent one cancer at 10 years as at approximately 5 years, the time of the early reports.