(Bloomberg) -- Bluebird Bio Inc. fell the most ever after its new gene therapy for sickle cell disease was approved in the US with caveats that may limit revenue.

The treatment, Lyfgenia, was approved by the Food and Drug Administration Friday with a boxed warning — the FDA’s most severe form of caution — saying that blood cancers have occurred in patients taking the therapy. That risk may push doctors to favor another sickle cell treatment approved at the same time.

Read More: First Crispr Therapy Gets FDA Nod for Sickle Cell Disease

The other therapy doesn’t carry a boxed warning and is also less expensive. Casgevy, made by Crispr Therapeutics AG and Vertex Pharmaceuticals Inc., will cost $2.2 million, compared with a $3.1 million price tag for Lyfgenia.

“Overall, we see an uphill commercial battle” for Bluebird, RBC Capital Markets analysts wrote in a note to clients, noting most doctors will likely favor Casgevy.

Bluebird shares fell 41% Friday, their biggest drop since the stock began trading a decade ago. The Cambridge, Massachusetts-based company has lost 59% of its market value this year.

Making matters worse for Bluebird, the company said it didn’t receive a priority review voucher from the FDA along with the approval. Bluebird had already lined up a buyer for the voucher and was expecting to get $103 million for it.

Bluebird investors have weathered a series of setbacks. The company faced safety issues and delays en route to getting FDA approval, and it nearly ran out of money last year.

“It remains unclear if Bluebird will be able to successfully transition into a profitable, commercial-stage company and compete with commercial giant Vertex in the sickle cell disease space,” William Blair analysts wrote in a research note.

The company has enough cash to last into the second quarter of next year, Bluebird Chief Executive Officer Andrew Obenshain said on a call with analysts. “We’re always exploring additional financing opportunities,” he said.

(Updates with company comment in ninth paragraph.)

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