Table 1 Distinction of benign and neoplastic myeloid proliferations
Benign | Neoplastic | |
|---|---|---|
Morphology | Unilineage proliferation: most commonly erythroid. Erythroid cells identifiable by hyperchromatic round nucleus with clear or pink ring of cytoplasm. Often present in clusters. Megakaryocytes identifiable by distinctive morphology; large size, multilobed nuclei, large amounts of granular cytoplasm. Multilineage proliferation: often all developmental stages of hematopoietic cells are seen, but predominantly mature forms. | Unilineage proliferation: typically monomorphous population of intermediate sized, noncohesive hematopoietic cells. Immature eosinophils are an important morphologic clue. Multilineage proliferation: most often seen in CMPD or MDS. Clusters of immature myeloid cells (eg blasts) may be seen. Megakaryocytes may be dysplastic; small or abnormally large size, hyperchromatic nucleus, hyper- or hypolobated nuclei, clustering. |
Immunohistochemistry | Rare or no expression of CD34, CD117, TdT | Diffuse positivity supports diagnosis of myeloid sarcoma, if other nonhematopoietic lesions or mastocytosis are not a diagnostic consideration. Expression of CD34 or CD117 in clusters may herald transformation of CMPD or MDS to blast phase or acute myeloid leukemia. |
Molecular/Genetic | No molecular or cytogenetic abnormalities expected. | Presence of cytogenetic abnormalities by conventional karyotype or FISH support a diagnosis of neoplastic proliferation. Specific defects (eg t(9;22) in CML) can confirm diagnosis. |
