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 often more important than data from randomized trials because of the inherent restrictions on sample size. The article provides clear information regarding the different behaviors of different histological types of sarcoma, the importance of localized therapy for metastatic disease, and the critical role of combination chemotherapy in initial treatment to improve survival.Please see related article: https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-017-0831-7.