Very rare diseases in oncology

Chen et al. [1] presented an important study on potential molecular prognostic predictors of recurrence in sacral chordoma. I wish to draw the readers’ attention to epidemiological and related socioeconomic and ethical issues of such a rare diagnosis. Various definitions for sporadic diseases have been proposed based on different cutoff incidence or prevalence rates. Some of these definitions delineate a substantial portion of the overall population disease burden. The apparent complexity of the group of rare diseases implies further explorations including the most uncommon entities.