Retrophin said its drug for a rare kidney disorder, which has no specific treatment, was found safe and effective in a mid-stage study, sending the company’s shares soaring as much as 44% on Wednesday.

Analysts said the efficacy and safety profile of the drug, sparsentan, exceeded expectations, keeping them optimistic about the possibility of an accelerated approval for a drug they estimate could rake in up to $1 billion in peak sales.

Retrophin—founded in 2008 by Martin Shkreli, who last year became a lightning rod for criticism of soaring drug prices—plans to discuss an expedited path for sparsentan with U.S. health regulators in the coming months, Chief Executive Stephen Aselage said.

Sparsentan was tested on 109 patients with focal segmental glomerulosclerosis (FSGS), which is characterized by progressive kidney scarring and often leads to kidney failure.

While FSGS has no specific treatment, sparsentan is designed to treat proteinuria, or excess serum protein in the urine, a key driver of FSGS. The drug aims to lower patients’ proteinuria levels, thereby reducing their risk of progressing to kidney failure.

Retrophin rtrx said a pooled analysis of patients given either a 200, 400, or 800 mg-per-day dose of sparsentan showed a 44.8% mean reduction in proteinuria after eight weeks.

That compared with an 18.5% reduction in patients given irbesartan, a generic drug used in lieu of an approved FSGS therapy, the company said.

However, each of the individual doses of sparsentan did not achieve statistically significant improvement over irbesartan, despite clear signs of relative benefit, Retrophin said.

BMO Capital Markets analyst Do Kim said the performance of each individual dose was not part of the criteria the drug was required to achieve in the trial.

Kim, like other analysts, said he remained optimistic that sparsentan could secure an accelerated approval, “although there’s nothing set in stone.”

FSGS affects up to 40,000 people in the United States, and analysts expect Retrophin can charge between $100,000 and $150,000 per patient per year if sparsentan is approved.

Retrophin, which already has three drugs on the market, licensed the rights to sparsentan from Ligand Pharmaceuticals in 2012. Shkreli led Retrophin till 2014. Shkreli, a hedge fund manager, was later accused of using the company a his personal bank account, using it to pay back his and his investors debts.

Ligand lgndz is eligible to receive a 9% royalty on sales of the drug, which was originally developed by Bristol-Myers Squibb bmy .

Retrophin shares were up about 38% at $22.47, easing off from a session high of $23.51. Ligand’s were up about 6%.