- Must have either bilateral or unilateral bone marrow aspiration and biopsy ≥ 42 days before first course of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) therapy (or CHOP plus rituximab [CHOP-R] for CD20+ disease) OR within 42 days prior to registration if CHOP/CHOP-R therapy has not begun