Currently in oncology a novel agent entering development has only 5% chance of making it to commercial use. One of the ways to mitigate this problem would be to conduct exploratory or 'phase 0' clinical trials, conducted before phase 1 dose-escalation safety and tolerance studies. These phase 0 studies are a first administration of the novel agent to humans, at limited doses, on a small number of patients and over a short period. The objectives are to validate preclinical development and to acquire pharmacokinetic and pharmacodynamic data in order to better justify the scientific rational. In this article, we focus on phase 0 trials and their usefulness for the development of new drugs in oncology. We performed a literature review of questions related to phase 0 trials in articles published during 2006 to 2009. Thirty articles on phase 0 clinical trials have been published. The affected fields are oncology and pharmacology. Phase 0 clinical trials are discussed in the literature in terms of theoretical issues and from academic, pharmaceutical industry and patient point of views. If phase 0 clinical trials are a future prospect for drug development against cancer, the clinical applications of these trials need to be specified.