Mielosarcoma – morphology, diagnosis

Mielosarcoma – morphology, diagnosis

Melosarcoma. This form is included in the WHO classification in the section of acute non-lymphoblastic leukemia (ONLL):

• extramedullary tumor from blast or maturing myeloid cells in patients with various myeloproliferative diseases or myelodysplastic syndromes;
• the presence of myelosarcoma in patients with acute non-lymphoblastic leukemia (ONLL) may be the first manifestation of the disease or a relapse of ONLL during remission. In patients with myeloproliferative diseases, it is associated with the onset of a blast crisis;
• blasts are more often represented by myeloblasts, but they can be cells of any myeloid line;
• type of blasts is determined on the basis of morphocytochemical and immunological studies;
• myeloblasts with maturation can have a translocation (8; 21), myelomonoblasts with eosinophils – inv16 or t (16; l6), monoblasts – anomaly 11q23.

The determination of the type of blast cells and, accordingly, the variant of acute non-lymphoblastic leukemia (ONLL) is based on the complex characteristics of the morphological, cytochemical and immunophenotypical features of leukemic elements.

The morphological criteria for the characteristics of blasts include cell size (ratio of macro-, meso- and microforms), the shape of nuclei (round, folded, monocytoid), the presence of grain and / or Auer rods, nuclear-cytoplasmic ratio (high, moderate or low). It is on the basis of morphological signs that leukemic myeloblasts and monoblasts are divided into cells with the presence or absence of signs of maturation.

Cytochemical markers of granulocyte blasts are peroxidase, lipids detected by Sudan black B, and ASD-chloroacetate esterase. The content of these markers in myeloblasts varies considerably, sometimes only one of them is detected. In the case of a dubious response, it is imperative to carry out two cytochemical reactions – peroxidase and lipids, in order to avoid a possible error.

The activity of ASD-chloroacetate esterase is significantly lower than peroxidase, therefore the definition of this enzyme is of lower diagnostic value. Low peroxidase activity in myeloblasts is a poor prognostic sign.

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