A mature B- or T- cell leukemia with progressive clinical course. It is characterized by the presence of medium-sized lymphocytes with visible nucleoli (prolymphocytes) in the peripheral blood, bone marrow, and spleen. The disease is Monarch Disease Ontology term MONDO_0001023 (prolymphocytic leukemia). Also known as: PLL, prolymphocytic leukaemia (B or T), prolymphocytic leukaemia (B or T-cell), prolymphocytic leukemia (B or T), prolymphocytic leukemia (B or T-cell).