B-cell prolymphocytic leukemia (Monarch Disease Ontology term MONDO_0019461) is a neoplasm of prolymphocytes affecting the blood, bone marrow, and spleen. It is characterized by prolymphocytes exceeding 55% of the lymphoid cells in the blood and profound splenomegaly. Also known as: B prolymphocytic leukaemia, B prolymphocytic leukemia, B-PLL.