70 year old male presented with 3-months history of generalised weakness. On examination, bilateral axillary lymphadenopathy was noted. Histopathological examination of enlarged lymph node showed effacement of lymph node architecture by diffuse proliferation of small-sized, mature-appearing lymphoid cells. Peripheral blood showed lymphocytosis with presence of CD5-positive and CD23-positive B-cells. Which of the following is the most likely diagnosis of this patient?

Chronic lymphocytic leukemia (CLL) CLL is the most common leukemia of adults in the Western world. Median age at diagnosis is 60 years. In CLL, absolute lymphocyte count is more than 5000/cumm. Lymph nodes are diffusely effaced by predominantly small lymphocytes. When present, proliferation centers are pathognomonic for CLL/SLL. The tumor cells express the pan B-cell markers CD19 and CD20, as well as CD23 and CD5. Burkitt lymphoma/leukemia - Adolescents or young adults with extranodal masses; uncommonly presents as "leukemia"; aggressive DLBCL - relatively large cell size (usually four to five times the diameter of a small lymphocyte) and a diffuse pattern of growth. CD5 and CD23 negative. Hodgkin lymphoma - arises in a single node or chain of nodes and spreads first to anatomically contiguous lymphoid tissues. Morphologically, the distinctive feature of Hodgkin lymphoma is the presence of neoplastic giant cells called Reed-Sternberg cells.