GSK Shares Plummet After FDA Panel Votes Against Blenrep Approval

GlaxoSmithKline Plc (GSK) experienced a significant decline in share price following an unfavorable recommendation from a United States Food and Drug Administration (FDA) advisory panel regarding its blood cancer treatment, belantamab mafodotin, marketed as Blenrep. This development represents a setback in GSK’s efforts to reintroduce the drug to the United States market after its voluntary withdrawal in 2022.

Blenrep is an antibody-drug conjugate designed to target multiple myeloma, a form of blood cancer affecting plasma cells in the bone marrow. Initially granted accelerated approval by the FDA in 2020 for patients with relapsed or refractory multiple myeloma, the drug was withdrawn from the United States and European markets in 2022 after a confirmatory late-stage trial failed to demonstrate superiority over existing therapies. GSK has since sought full approval for Blenrep in combination regimens: one with bortezomib (generic Velcade) and dexamethasone, and another with pomalidomide (Pomalyst, marketed by Bristol Myers Squibb) and dexamethasone. These combinations have already received approvals in the United Kingdom and Japan.

The FDA’s Oncologic Drugs Advisory Committee convened on July 17, 2025, to evaluate these applications. The panel voted 5-to-3 against recommending approval for the Blenrep-Velcade combination and 7-to-1 against the Blenrep-Pomalyst regimen, concluding that the potential risks outweighed the demonstrated benefits. Primary concerns centered on severe ocular toxicities, including vision impairment and other eye-related side effects, which were deemed significant despite GSK’s arguments for the selected dosing. FDA staff had previously highlighted in briefing documents that lower doses might mitigate these risks while maintaining efficacy, raising questions about the appropriateness of the proposed regimen. Although the panel’s recommendation is non-binding, the FDA typically aligns with such advisories, with a final decision anticipated by July 23, 2025.

In response to the panel’s vote, GSK’s shares declined by approximately 6% on July 18, 2025, positioning the company at the bottom of the FTSE 100 index. This drop reflects investor concerns over the potential rejection’s impact on GSK’s oncology pipeline, which has been a focus area for growth under Chief Executive Officer Emma Walmsley. GSK has not issued detailed public statements in the immediate aftermath. Still, company representatives defended the drug’s risk-benefit profile during the advisory meeting, emphasizing its potential value for patients with limited treatment options.

This outcome underscores ongoing challenges in oncology drug development, particularly balancing efficacy against safety in advanced therapies. Should the FDA reject the applications, GSK may explore dose adjustments or additional studies to address the concerns, though no specific plans have been announced as of July 18, 2025.