The leukemia from which the human cell line HL-60 was derived was classified in 1976 as acute progranulocytic leukemia (APL), although it was recognized to show a number of atypical features. In the ensuing 10 years, the concept of APL and its integral association with t(15;17) has evolved, and the concept of APL as a morphologically recognizable entity has become embodied in the term French-American-British classification M3 (FAB-M3). It is now recognized that not every case of leukemia with a high proportion of progranulocytes can be classified as FAB-M3. We reviewed the light and ultrastructural morphology of the original diagnostic material from this case, and we report that the leukemia from which HL-60 was derived does not conform to the currently recognized entity of FAB-M3 and is more appropriately classified as an acute myeloblastic leukemia with maturation, FAB-M2.

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Twenty-six patients with inv(16)(p13q22) or del(16)(q22) in association with acute myelomonocytic leukemia (AMML-M4, FAB classification), and abnormal marrow eosinophils have been treated at this institute. Initial bone marrow eosinophilia (greater than or equal to 4%) was observed in 22 of 26 patients (85%), and abnormal eosinophil morphology, characterized by immature cells with some interspersed basophilic granules, was evident in 26 of 26 (100%). Giemsa-banded chromosome analysis performed in all patients revealed 16 cases with inv(16)(p13q22) alone, and ten cases with additional chromosome changes. Twenty-five patients received combination induction chemotherapy, and 23 (92%) achieved complete remission (CR). The median duration of remission was 18 months (range, six to 72 + months), and the median duration of survival was 34 months (range, 0.5 to 133 months). Nine patients (35%) relapsed in the CNS at a median time of 19 months (range, six to 133 months) from first marrow CR. All patients had leptomeningeal disease, and in addition, six of nine (66%) demonstrated two or more enhancing lesions on computed tomography brain scan, consistent with intracerebral myeloblastomas. Review of 384 Giemsa-banded patients with acute myeloid leukemia revealed no other morphologic or cytogenetic subgroup with either an equivalent incidence of CNS leukemia or documented intracerebral myeloblastomas. This series of inv(16)(p13q22)/del(16)(q22) AMML reports a favorable prognosis for such patients and associates a specific clonal cytogenetic subgroup of acute leukemia with a distinct propensity for CNS relapse, manifesting as leptomeningeal disease and intracerebral myeloblastomas.