AstraZeneca Plc said on Monday the U.S. drug regulator declined to approve its asthma medicine, Fasenra, for treatment of chronic rhinosinusitis with nasal polyps, a condition characterized by benign growths that cause pain and stuffiness.

Fasenra (benralizumab) is a monoclonal antibody that binds directly to IL-5 receptor alpha on eosinophils and attracts natural killer cells to induce rapid and near-complete depletion of blood and tissue eosinophils in most patients via apoptosis (programmed cell death). Nasal polyps are a strong indicator of the eosinophilic phenotype in severe asthma and response to Fasenra, including reductions in exacerbation and improvement in lung function.

The London-listed drugmaker said the U.S. Food and Drug Administration (FDA) had issued a complete response letter following AstraZeneca’s application to extend the use of the treatment and requested additional clinical data from it.

Fasenra was AstraZeneca’s first respiratory biologic and raked in $1.26 billion in sales in 2021, jumping 33% from the previous year. It belongs to a class of medicines called monoclonal antibodies and is used against severe asthma.

Fasenra is currently approved as an add-on maintenance treatment for severe eosinophilic asthma in the US, EU, Japan and other countries and is approved for self-administration in the US, EU and other countries.

The treatment rivals GlaxoSmithKline’s Nucala and Teva’s Cinqair is from the same drug class, while AstraZeneca has also developed a newer medicine, Tezspire, with Amgen which would compete with Fasenra.

The setback for AstraZeneca’s Fasenra comes after the drugmaker said on Friday the FDA had approved its and Merck’s cancer drug, Lynparza, as a treatment for patients with early-stage breast cancer with certain mutations, as previously reported.