SERB Pharmaceuticals Agrees to Acquire Y-mAbs Therapeutics

SERB Pharmaceuticals and Y-mAbs Therapeutics, Inc. recently announced they have entered into a definitive merger agreement under which SERB will acquire Y-mAbs, including its lead commercial oncology asset, DANYELZA (naxitamab-gqgk), in an all-cash transaction, representing an equity value for Y-mAbs of approximately $412 million.

Under the terms of the merger agreement, SERB will commence an all-cash tender offer to purchase all outstanding shares of Y-mAbs common stock. Holders of Y-mAbs common stock would receive $8.60 per share in cash, representing a premium of approximately 105% to Y-mAbs’ closing share price on August 4, 2025, the last full trading day prior to the transaction announcement.

The transaction was unanimously approved by the Y-mAbs Board of Directors following a review of strategic alternatives to maximize value for Y-mAbs stockholders, with the assistance of external advisors. The process included discussions with numerous potential buyers for Y-mAbs or for the DANYELZA or Radiopharmaceuticals businesses on a standalone basis. In addition, the Board reviewed potential sources of additional capital to support accelerating the further development of the company’s pipeline.

With a focus on pediatric oncology, Y-mAbs successfully developed and commercialized the anti-GD2 therapy, DANYELZA (naxitamab-gqgk). DANYELZA is the first FDA-approved treatment for relapsed or refractory high-risk neuroblastoma – a rare and aggressive pediatric cancer – and was approved in the United States under accelerated approval based on overall response rate and duration of response. DANYELZA is indicated for the treatment of pediatric patients one year of age and older and adult patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow who have demonstrated a partial response, minor response, or stable disease to prior therapy. In addition to inpatient use, doctors can choose to administer DANYELZA in an outpatient setting, which may reduce the logistical burden on patients and their families. Y-mAbs’ portfolio also includes an investigational therapy targeting GD2 in solid tumors and CD38 in circulating tumors in ongoing Phase 1 clinical trial from its Self-Assembly DisAssembly (SADA) Pretargeted Radioimmunotherapy Platform (PRIT).

Vanessa Wolfeler, Chief Executive Officer of SERB, said “High-risk neuroblastoma is not only a rare and devastating pediatric cancer but also one of the most difficult to treat. DANYELZA is recognized as a critical treatment option for patients and expands the treatment pathways available to providers in an outpatient setting. Working together with the team from Y-mAbs, I believe we can continue generating data for this product, expand partnerships to additional oncology centers, and have a positive impact on the lives of more neuroblastoma patients and their families.”

Jeremie Urbain, Chairman of SERB, added “Following SERB’s expansion into the United States five years ago, this acquisition reflects another milestone in the execution of our growth strategy to build a leading global specialty pharma platform. DANYELZA is an excellent strategic fit for SERB as it strengthens our existing rare oncology portfolio and will allow us to leverage our existing global footprint and our medical, regulatory, and commercial expertise to expand the reach of DANYELZA to new markets.”

SERB has a growing portfolio of medicines for rare emergency medicine, rare diseases, and CBRN preparedness, supplying healthcare providers around the world. The acquisition of DANYELZA broadens SERB’s existing Rare Oncology portfolio (Voraxaze, Vistogard, Xermelo) and furthers its mission of building a leading portfolio of medicines that improve the standard of care for patients globally.

Michael Rossi, President, Chief Executive Officer and a member of the Board of Directors, Y-mAbs, said “Our Board regularly reviews our business, including our strategy, the current state of the biopharmaceutical sector and the time and resources required to execute on our strategic plans. Following the thorough process to explore all of the potential paths forward for the company, we are now moving forward with this agreement with SERB that we believe reflects the most attractive option available to Y-mAbs, providing significant, immediate and certain value to our stockholders. This transaction is a testament to our team’s hard work in building a strong foundation as a commercial organization with a differentiated, FDA-approved product in DANYELZA. We believe that Y-mAbs has made important progress advancing DANYELZA and our Radiopharmaceuticals platform. By combining our expertise and resources with SERB’s specialty commercial capabilities, we can extend our shared commitment of improving the lives of even more patients and families on a global scale.”

Under the terms of the merger agreement, SERB is obligated to commence a tender offer by August 19, 2025, to purchase all of Y-mAbs’ outstanding shares for $8.60 per share in cash. Assuming a majority of the outstanding Y-mAbs shares are tendered into, and not withdrawn from, the tender offer, and subject to the satisfaction of other customary conditions, including the receipt of a majority of Y-mAbs shares in the tender offer and expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act, SERB is required to close the tender offer, following which, Y-mAbs will be merged with a subsidiary of SERB. After such merger, Y-mAbs shares that were not tendered in the tender offer will be converted into the right to receive the same $8.60 per share in cash paid for shares in the tender offer, and Y-mAbs’ stock will no longer be listed on the Nasdaq exchange.

Y-mAbs stockholders holding approximately 16% of Y-mAbs’ outstanding shares of common stock have entered into a tender and support agreement with SERB, pursuant to which such stockholders have agreed, among other things, to tender all of their shares of Y-mAbs common stock in the tender offer, subject to the terms and conditions of such agreement.

The transaction is expected to close by the fourth quarter of 2025.

Rothschild & Co. is acting as exclusive financial advisor, Freshfields US LLP is acting as legal counsel and H/Advisors Abernathy is acting as strategic communications advisor to SERB.

Centerview Partners is acting as exclusive financial advisor, Cooley LLP is acting as legal counsel and Joele Frank, Wilkinson Brimmer Katcher is acting as strategic communications advisor to Y-mAbs.

SERB is a global specialty pharmaceutical company with a growing portfolio of medicines for rare emergency medicine, rare diseases, and CBRN preparedness. For over 30 years we have made treating complex and life-threatening conditions possible, supporting clinicians, healthcare systems and governments while offering hope to patients and their families. The company’s Rare Oncology portfolio includes Voraxaze (glucarpidase), Vistogard (uridine triacetate), Xermelo (telotristat ethyl). SERB is also a leading provider of essential acute care medicines, addressing unmet medical needs and supplying antidotes and medical countermeasures for chemical, biological, radiological and nuclear (CBRN) risks. As a fully integrated company, we have the experience and capabilities to acquire, develop, and manufacture our medicines to the highest standards, and make them available worldwide through our secure supply chain. For more information, visit https://SERB.com.

Y-mAbs is a commercial-stage biopharmaceutical company focused on the development and commercialization of novel, radioimmunotherapy and antibody-based therapeutic cancer products. The company’s broad and advanced commercial product pipeline includes the anti-GD2 therapy DANYELZA (naxitamab-gqgk), the first FDA-approved treatment for patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow after a partial response, minor response, or stable disease to prior therapy. The company’s technologies include its investigational Self-Assembly DisAssembly (SADA) Pretargeted Radioimmunotherapy Platform (PRIT) and bispecific antibodies generated using the Y-BiClone platform.