A 52-year-old man from Delhi presents with a 3-month history of painless lymphadenopathy involving the neck, axilla, and groin. On examination, he has firm, mobile, non-tender lymph nodes. Laboratory investigations show hemoglobin 11.2 g/dL, WBC 7,200/μL, and platelets 180,000/μL. LDH is elevated at 580 U/L. A lymph node biopsy is performed and histopathology reveals diffuse proliferation of small lymphocytes with scant cytoplasm, coexpressing CD5 and CD19. Flow cytometry confirms CD5+, CD19+, CD23+ B cells. What is the most appropriate next step in management?