Monarch Disease Ontology id MONDO_0018689 (plasma cell leukemia) is an aggressive plasma cell neoplasm characterized by the presence of neoplastic plasma cells in the peripheral blood. It is characterized by the presence of a circulating clonal plasma cell count that exceeds 2x10^9/L or is 20% of the leukocyte differential count. Also known as: PCL, leukaemia plasmacytic, leukemia plasmacytic, plasmacytic leukaemia, plasmacytic leukemia.