Current controversies in the application of meta-analysis (with special reference to oncological treatments)

Meta-analysis was proposed more than 20 years ago as an innovative technique for pooling the results of a series of clinical studies. This technique has a two-fold purpose: i) to retrieve pertinent clinical information without introducing selection biases; ii) to combine these clinical data obtained from different sources into a single synthetic index that summarises all available information. This review highlights the current perspectives in the application of meta-analysis and places particular emphasis on discussing the limitations of this technique that have been identified in recent years. Specific controversies in this area include: i) comparison between meta-analysis of the literature and meta-analysis of individual patient data; ii) heterogeneity of the clinical material introduced in the meta-analytic pooling; and iii) survival meta-analysis as a method for pooling long-term outcome data. After debating these three controversial points, this review examines the newest uses of meta-analysis that have been proposed for the evaluation of cost-effectiveness data and tries to identify the meta-analytic applications that will probably be expanded in the near future as opposed to those that will instead be developed less and less.