Almost every new drug approved by the FDA in the last three years with a price tag of at least  $100,000 per patient per year had a rare disease designation, according to new findings from life sciences consulting firm Trinity Partners.

The FDA’s rare-disease designation, also called orphan status, grants drugmakers developing drugs that treat rare or orphan diseases and conditions certain development incentives, like tax credits for some clinical testing, if they qualify.  

“We were really trying to look at what some of the most expensive drugs were in the past three years and try to tease out some of the of characteristics, and also find out what people are willing to pay for,” said Jillian Godfrey Scaife, principal at Trinity Partners and co-author of the report.

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The archetype for the most expensive novel drugs over the last three years were treatments for rare diseases, pediatric patients, that are dosed chronically, and were first-in-class.

The firm looked at wholesale acquisition prices for all 103 novel drugs — as designated by the FDA’s Center for Drug Evaluation and Research — from 2014 to 2016. In that three-year period, 91%, or 31 out of 34 drugs, priced at or above $100,000 per patient per year had a rare-disease designation.

The analysis found 10 products were priced at $200,000 per patient per year and 24 products were priced between $100,000 to $200,000 per patient per year.

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Every product priced at $200,000 per patient per year had a rare-disease designation. Some examples include Sarepta Therapeutics’ Exondys 51 for Duchenne muscular dystrophy, Vertex Pharmaceuticals’ Orkambi for cystic fibrosis, and Genzyme’s Cerdelga for Gaucher disease for adults.

Of the 24 drugs that were priced between $100,000 to $200,000, only three drugs did not have a rare-disease designation — Roche’s bladder cancer drug Tecentriq, Pfizer’s breast-cancer drug Ibrance, and Novartis’s Odomzo. Furthermore, Trinity found that 46 — or 45% — of all novel drugs approved by the FDA between 2014 and 2016 were for rare diseases.

Orphan drug sales are expected to reach $178 billion by 2020, according to EvalutePharma’s most recent drug report, and the sales of those therapies are forecast to become 20% of all prescription drug spending by 2020.

As to why they’re priced so high, Godfrey Scaife said that one “has to take into account the patients indicated for that disease. For some of their rare conditions it costs a lot of money to develop these therapies” and sometimes “there’s very few patients who are able to treated with it.”