ALK-negative anaplastic large cell lymphoma with extensive peripheral blood and bone marrow involvements manifested as "leukemic phase".

CD30-positive anaplastic large cell lymphoma (ALCL) is a distinctive malignant large cell lymphoma of T-cell lineage, often presenting in lymph node or extranodal sites. ALCL cases with extensive bone marrow and peripheral blood involvement manifested as "leukemic phase" are extremely rare and the most of those cases reported are anaplastic large cell lymphoma kinase (ALK) positive ALCL in childhood population. Here we report four adult cases of ALK-negative ALCL with extensive bone marrow and peripheral blood involvement manifested as "leukemic phase". Circulating large lymphoma cells varied from 20 to 80% in peripheral blood and bone marrow biopsy showed various nodular or interstitial infiltrates. By reviewing the clinicopathologic data of previously reported ALCL cases with extensive bone marrow and peripheral blood involvement, there appears to be of large variations in regard to the patient's age, morphologic variants, immunophenotypic or genotypic characteristics of the disease. While most cases of ALCL with peripheral blood and bone marrow involvement were ALK-positive or carrying t(2;5) translocation, rare ALK-negative cases were also present. Leukemic ALCL patients usually have unfavourable prognosis, regardless of ALK expression.