Hematologic Malignancies USMLE Step 1 Practice Question

A 45-year-old man presents with a 2-week history of rapidly enlarging jaw swelling, fever, night sweats, and abdominal pain. Temperature is 38.5°C, heart rate 105/min. Physical examination reveals a large, firm, fixed mass involving the angle of the mandible and palpable abdominal masses. Laboratory studies show hemoglobin 11.2 g/dL, platelets 95,000/μL, and LDH 4,100 U/L. CT imaging demonstrates involvement of the jaw, small bowel, and mesentery with minimal ascites. Bone marrow biopsy shows monomorphic proliferation of medium-sized lymphocytes with scant cytoplasm, high mitotic rate, and expression of CD20+, CD10−, and BCL6+. Cytogenetic analysis reveals t(8;14)(q24;q32). Which of the following is the most likely diagnosis?