Omeros Stock Jumps Premarket After FDA Approves First Drug For Rare Transplant Complication — Retail Sees Big Upside

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The drug was approved for use in adults and children aged two years and older.

  • The FDA approval clears the path for a U.S. launch in January 2026.
  • Trial and expanded access data showed strong response rates and short-term survival in high-risk patients.
  • Yartemlea becomes the first and only FDA-approved treatment for TA-TMA.

Shares of Omeros Corporation (OMER) jumped 8% in premarket trading on Monday after the U.S. Food and Drug Administration approved its drug Yartemlea (narsoplimab-wuug) for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy, or TA-TMA. 

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First And Only Approved Therapy For TA-TMA

The approval makes Yartemlea the first and only therapy specifically indicated for TA-TMA and clears its use in adults and children aged two years and older.

TA-TMA is an often-fatal complication following stem cell transplantation. Omeros said Yartemlea works by selectively inhibiting MASP-2, the effector enzyme of the lectin pathway of complement, while preserving classical and alternative complement functions important for host defense.

Omeros said it is finalizing preparations for a U.S. launch of Yartemlea in January 2026. 

Clinical Trial Results

Approval by the U.S. Food and Drug Administration was based on data from a single-arm, open-label pivotal study in 28 adults with TA-TMA, supported by additional results from a global expanded access program that included adult and pediatric patients.

In the trial, 61% of patients had a complete response, meaning their key lab test results improved and they either showed better organ function or no longer needed blood transfusions. Among patients with response data in the expanded access program, the complete response rate was 68%.

Across both datasets, 100-day survival from the time of TA-TMA diagnosis was 73% in the study and 74% in the expanded access program. All patients met international criteria for high-risk TA-TMA, a group associated with poor prognosis and high risk of death.

Survival Benefit 

Omeros said peer-reviewed publications have shown treatment with Yartemlea was associated with a three to four-fold lower risk of mortality compared with a well-matched external control group receiving supportive care.

In patients who had failed or discontinued prior off-label therapies, including other complement inhibitors or defibrotide, Yartemlea treatment was associated with nearly 50% one-year survival, compared with historical rates reported at less than 20%.

How Did Stocktwits Users React?

On Stocktwits, retail sentiment for Omeros was ‘extremely bullish’ amid ‘extremely high’ message volume.

OMER sentiment and message volume as of December 24| Source: Stocktwits

One user said the stock could move above the $20 level following the approval of the company’s drug, adding that a short squeeze early in the session could push shares higher. The stock ended Tuesday’s session at $8.75.

Another user celebrated the approval saying, “Congratulations and Merry Christmas to Omeros and all longs many like me that have waited for this event that seemed like would never come.”

Omeros’ stock has declined 8% so far in 2025.

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