Light micrograph of small lymphocytic lymphoma involving the lungs. The alveolar septa and peribronchial and perivascular areas are expanded by nodular aggregates of small mature lymphocytes. This was an incidental finding in a known case of chronic lymphocytic leukaemia. B-cell chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) are the most common mature B-cell neoplasms and considered to be different manifestations of the same disease. In contrast to CLL, SLL is much less common, making up only about 4% of non-Hodgkin lymphomas. The distribution of the neoplastic cells in SLL is mainly extramedullary with very few leukemic cells in blood.