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Acute promyelocytic leukaemia: a study of 39 cases with identification of a hyperbasophilic microgranular variant
Abstract:
Thirty-nine cases of acute promyelocytic leukaemia (APL) were divided into two morphological subgroups, typical hypergranular APL (31 cases) and microgranular APL (eight cases, 21%). The leukaemic cells in the microgranular APL cases were characterized by striking nuclear folding or lobulation; granulation was present in most of these cells but was less abundant and finer than in typical APL. In three microgranular APL cases a distinctive small leukaemic promyelocyte with unusual nuclear lobulation and deeply basophilic cytoplasm containing few or no visable granules was the predominant leukaemic cell. This small hyperbasophilic promyelocyte was also present as a minor population of cells in the other five microgranular APL case and in 28 of the 31 typical APL cases. Ultrastructurally the most abundant promyelocytes in microgranular APL had smaller and usually fewer granules than in typical APL; other characteristic ultrastructural features of APL were found with equal frequency. The median blood leucocyte count was significantly higher in microgranular APL, 83.0 x 10(9) x 10(9)/l, than in typical APL, 1.8 x 10(9)/l (P less than 0.01). The median duration of complete remission (CR) for microgranular APL, 6.5 months, was shorter than the 21 + month median CR for typical APL. The morphological characteristics of microgranular APL may mimic those of myelomonocytic leukaemia; however, the presence of cells with multiple Auer rods, large inclusions of Auer-like material and the small hyperbasophilic promyelocytes are important distinguishing features. In equivocal cases cytochemistry, electron microscopy and cytogenetic studies may verify the diagnosis.
Insights
This study differentiates between typical and microgranular acute promyelocytic leukemia (APL) subtypes. Microgranular APL shows distinct morphological features and a poorer prognosis, necessitating accurate diagnosis for effective treatment.
Area of Science:
- Hematology
- Oncology
- Cell Biology
Background:
- Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia.
- Morphological variations within APL can impact clinical presentation and outcomes.
- Distinguishing between APL subtypes is crucial for appropriate management.
Purpose of the Study:
- To investigate and compare the morphological, ultrastructural, and clinical characteristics of typical hypergranular APL and microgranular APL.
- To identify key features that differentiate microgranular APL from other myeloid leukemias.
- To assess the prognostic implications of morphological subtypes in APL.
Main Methods:
- Morphological classification of 39 APL cases into typical hypergranular (31) and microgranular (8) subgroups.
- Detailed analysis of nuclear and cytoplasmic features of leukaemic cells.
- Ultrastructural examination of promyelocytes.
- Comparison of clinical parameters including white blood cell count and duration of complete remission.
Main Results:
- Microgranular APL cases exhibited distinct nuclear folding/lobulation and reduced/finer granulation compared to typical APL.
- A small hyperbasophilic promyelocyte was identified as a key feature in microgranular APL.
- Microgranular APL showed significantly higher median white blood cell counts and shorter median complete remission durations.
- Ultrastructural findings confirmed differences in granule content between the two subtypes.
Conclusions:
- Microgranular APL represents a distinct morphological variant with unique cellular characteristics.
- Key distinguishing features of microgranular APL include specific nuclear morphology and the presence of small hyperbasophilic promyelocytes.
- The observed differences in clinical parameters suggest a potentially poorer prognosis for microgranular APL.
- Diagnostic aids like cytochemistry, electron microscopy, and cytogenetics are valuable in equivocal cases.