Editorial note : Nature : Nature Publishing Group

In their Comment article 'Raise standards for preclinical cancer research', C. Glenn Begley and Lee Ellis (Nature483, 531–533; 2012) refer to scientists at Amgen who were able to reproduce findings in only 11% of 53 published papers. Several correspondents have asked for details of these studies, which were not provided in the article.

The Amgen scientists approached the papers' original authors to discuss findings and sometimes borrowed materials to repeat the experiments. In some cases, those authors required them to sign an agreement that they would not disclose their findings about specific papers. Begley and Ellis were therefore not free to identify the irreproducible papers — a fact that the Comment should have mentioned.

Nature, like most journals, requires authors of research papers to make their data available on request. In this less formal Comment, we chose not to enforce this requirement so that Begley and Ellis could abide by the legal agreements.

The scientists at Amgen could not have implemented their study had they reserved the right to reveal the outcome for individual papers. The Comment highlights important systemic problems in preclinical cancer research, which we felt appropriate to communicate to our readers, even though the authors could not disclose the studies in question.