A 45-year-old woman presents with fatigue, weight loss, and swollen lymph nodes. Blood tests reveal elevated levels of monoclonal antibodies. What condition does she most likely have?

• A. Common variable immunodeficiency (CVID)
• B. Hyper-IgM syndrome
• C. Multiple myeloma
• D. Systemic lupus erythematosus (SLE)

Answer: (C)