C33-22 Chemotherapy-induced Eosinophilia Leading to Refractory Asthma Exacerbations Successfully Treated With Benralizumab

Abstract Introduction Eosinophilia is a recognized but uncommon adverse effect of several chemotherapeutic and targeted agents. While most cases are transient and asymptomatic, a subset may lead to clinically significant end-organ manifestations including respiratory complications. We describe a unique case of recurrent asthma exacerbations driven by severe chemotherapy-induced eosinophilia, successfully treated with an anti-interleukin-5 receptor monoclonal antibody (Bernalizumab). Case Description A 48-year-old woman with metastatic HER2-positive breast cancer was receiving combination therapy with trastuzumab, pertuzumab, paclitaxel, and letrozole. She had a remote history of mild, well-controlled asthma. During the course of therapy, she developed progressive eosinophilia with her absolute eosinophil count rising from 0.5 × 109/L to 8.1 × 109/L. This coincided with recurrent asthma exacerbations characterized by wheezing, dyspnea, and elevated fractional exhaled nitric oxide levels, refractory to multiple prednisone bursts and optimized inhaled corticosteroid-long-acting beta-agonist therapy. A comprehensive evaluation excluded parasitic infection as a secondary cause of eosinophilia. Given her ongoing oncologic therapy and the risks of chronic immunosuppression, a multidisciplinary risk-benefit discussion was held with oncology and pulmonary teams. She was initiated on benralizumab (Fasenra), an anti-IL-5 receptor monoclonal antibody that depletes eosinophils via antibody-dependent cytotoxicity. Her symptoms improved markedly, eosinophil count normalized, and she remained free of further exacerbations over the ensuing six months while continuing cancer therapy. Discussion This case illustrates a rare but clinically important manifestation of chemotherapy-associated eosinophilia resulting in severe, steroid-refractory asthma. Among chemotherapeutic regimens, taxanes and monoclonal antibody combinations (such as trastuzumab and pertuzumab) have been implicated in hypersensitivity-like eosinophilic reactions. The use of targeted anti-IL-5 biologic therapy in this context is novel and highlights a potential steroid-sparing strategy when eosinophilia-driven airway inflammation complicates cancer treatment. Clinicians should maintain vigilance for new or worsening asthma symptoms in oncology patients with rising eosinophil counts, as timely recognition and intervention can prevent morbidity without interrupting life-prolonging chemotherapy. Learning Point Chemotherapy-induced eosinophilia can exacerbate underlying asthma and mimic disease progression; anti-IL-5 biologics such as benralizumab may offer effective and safe eosinophil control when corticosteroids are inadequate or contraindicated. This abstract is funded by: None