Successful obinutuzumab desensitization following immediate hypersensitivity reaction in a patient with marginal zone lymphoma

Obinutuzumab is a humanized anti-CD20 monoclonal antibody widely used in the treatment of B-cell lymphomas. Infusion-related reactions may limit its use and compromise optimal oncologic management. Drug desensitization represents an effective strategy to allow continuation of first-line therapy in selected patients. Case report: We report a patient with marginal zone lymphoma who developed an immediate hypersensitivity reaction during the first infusion of obinutuzumab, characterized by generalized erythematous rash, pruritus, urticaria, dyspnea, nausea, and oxygen desaturation. At the time of the reaction, vital signs were as follows: blood pressure 105/67 mmHg, heart rate 92 beats/min, and oxygen saturation 87% on room air. According to the Brown severity classification, the reaction was classified as moderate anaphylaxis (Grade 2) because there was respiratory involvement without persistent hypotension, collapse, or neurological compromise despite transient oxygen desaturation. Skin prick and intradermal tests were conducted using dilutions of 1/1 (25 mg/mL), 1/10 (2.5 mg/mL), 1/100 (0.25 mg/mL), and 1/1000 (0.025 mg/mL) prepared similarly to other biologic agents. Skin tests performed with dilutions prepared 4 weeks after the reaction were found to be negative. Given the clinical necessity of continuing treatment, a modified desensitization protocol was performed under close monitoring. Mild breakthrough reactions occurred during the initial desensitization steps but were successfully managed. Subsequent infusions were completed without further adverse reactions. Conclusion: This case highlights the feasibility and safety of obinutuzumab desensitization in patients with immediate hypersensitivity reactions. Given the limited number of reported cases in the literature, this report provides valuable clinical evidence supporting individualized desensitization strategies.