Orphan drug development takes 18 percent longer to reach the product launch stage than new drugs across the board, according to a new analysis from the Tufts Center for the Study of Drug Development.

Researchers examined 46 first-in-class orphan drugs approved by the FDA between 1999 and 2012 and found that orphan drugs take an average of 15.1 years to run the gauntlet from first patent filing to launch. The average time for new drugs across the board, meanwhile, is only 12.8 years. “Ultra-orphan” drugs for patient populations of only a few hundred can take an average of 17.2 years.

The analysis also found that oncology drugs were the fastest to navigate the approval process. In 2016, 125 oncology drugs were designated orphan drugs, while 17 were approved. In the same year, nine cardiovascular drugs were designated orphan drugs and two approved, while 53 central nervous system drugs were designated and three approved.

The emphasis on oncology drugs, the report states, is largely due to increased understanding of how cancer progresses and a more advantageous reimbursement environment.