Interest in developing drugs for orphan diseases is expected to grow into the next decade, leading to orphan drugs making up 19 percent of all prescription sales by 2020, according to some estimates.

Sales also could increase at a rate of almost 11 percent per year through the end of the decade, almost three times the annual 4 percent growth rate for drugs that treat larger populations, notes EvaluatePharma’s Orphan Drug Report 2014.

Pharmaceutical companies are drawn to the orphan drug market because of low development costs and often high returns. Trials involve smaller populations and often there are tax incentives. Because there is no alternative treatment, orphan drugs often are not subject to competition from generics and command higher prices: on average, six times more per patient than drugs for non-orphan diseases, the report states.

While the outlook is good now for orphan drugs, sales may be slowed in the coming years if payers start to look for ways to reduce drug costs.