FDA approves $2.8 million gene therapy

• It's only the third gene therapy approved by the FDA.

Details: Bluebird estimates there are between 1,300 and 1,500 people with beta-thalassemia, also known as beti-cel.

• The company plans to use an outcome-based agreement, saying it'll reimburse insurers up to 80% of the cost of the therapy for any patients who still need regular transfusions after their treatment.

What they're saying: The Institute for Clinical and Economic Review, a group that evaluates drug pricing and effectiveness, said in a statement the drug has high long-term value, even with a price tag over $2 million.

The bottom line: Gene therapies offer a particular source of promise for treating rare diseases. But they've proved costly so far and the growing pipeline of such treatments could lead to staggering health care spending.