Observational studies: goldmines of information on rare diseases

The article by Savina et al. from the large METASARC database of the French Sarcoma Group (BMC Med 15:78, 2017) provides a wealth of information about the natural history and therapy of patients with metastatic soft tissue sarcomas. The information complements - and in some cases surpasses - that obtained from randomized clinical trials, and should not be overlooked because of its retrospective nature. For rare diseases, retrospective data are...