A proposed definition of rare diseases for China: from the perspective of return on investment in new orphan drugs

A prevalence threshold to define rare diseases is needed for orphan drug designation. Here, we propose a bottom-up approach to defining rare diseases for China, based on the minimum number of patients needed for the industry to make a reasonable profit on a new drug. To obtain this patient population size, we considered three factors: (1) the industry research and development cost per new drug; (2) the sales per new drug to recoup its research and development costs and generate profit; (3) the highest affordable cost for one patient's treatment in a given healthcare system. Using this model, we estimate that, with the current level of innovation in the pharmaceutical industry in China, between 300,000 and 500,000 patients could be a reference threshold to define rare diseases. Compared with other proposals, this evidence-based definition is more useful for designing rare diseases and orphan drug policies for China.