Missing data in biologic oncology products.

The intent-to-treat principle requires analyses according to the treatment groups to which patients were randomized and that patients be followed to the occurrence of the endpoint or the end of study. This provides unbiased comparisons with valid p values. For many trials the limitations of the data will not be known until the data are analyzed. In this article, the loss-to-follow-up with respect to the intent-to-treat principle on the most important efficacy endpoints was evaluated for clinical trials of anticancer biologic products submitted to the FDA from August 2005 to October 2008. We provide recommendations in light of the results.