Supplemental material for: Progression of IgA-κ Monoclonal Gammopathy to Symptomatic Multiple Myeloma During Nivolumab Therapy for Melanoma: A Case Report

During treatment, he developed progressive back pain, fatigue, impaired mobility, and confusion. On April 30, 2024, hemoglobin was 7.7 g/dL, creatinine 2.65 mg/dL, calcium 15.2 mg/dL, and IgA 1,970 mg/dL. Imaging demonstrated vertebral compression fractures and diffuse skeletal abnormalities.

Bone marrow core biopsy showed 40% κ-restricted CD138-positive plasma cells with aberrant CD56 expression. Nivolumab was discontinued, and bortezomib, cyclophosphamide, and dexamethasone were initiated. IgA decreased to approximately 510 mg/dL by October 2024, although persistent κ excess remained on later testing.</p><p dir="ltr">Conclusion: The chronology raises the hypothesis that PD-1 blockade may have accelerated an already evolving plasma-cell clone, but the pre-treatment anemia, incomplete surveillance, and absence of baseline marrow and free-light-chain data preclude causal attribution.

Baseline characterization and continued hematologic monitoring may be appropriate when checkpoint inhibitors are given to patients with known monoclonal gammopathies.</p>