A man aged 68 complains of tiredness, sweating, enlargement of cervical, submaxillary and axillary lymph nodes. Blood tests: WBC - 35×109/l, lymphocytes - 60%, Botkin and Gumprecht bodies, level of haemoglobin and quantity of thrombocytes is normal. Myelogram showed 40% of lymphocytes. What is the most probable diagnosis?