Myeloid sarcomas, also called granulocytic sarcomas, chloromas, or extramedullary myeloid tumors, are rare extramedullary masses comprised of myeloid precursor cells. Most commonly, these tumors happen in association with acute myeloid leukemia (AML), but they may also occur with other myeloproliferative and myelodysplastic disorders.
Different from leukemic infiltrates, myeloid sarcomas characteristically efface the involved tissue architecture, and are recognized as a distinct entity by the WHO classification of tumors of hematopoietic and lymphoid tissues.
It is more commonly seen is in children, with ~60% occurring in individuals less than 15 years of age. There is no recognized gender predilection.
Myeloid sarcoma may develop during the course of a hematologic disorder but is seen to precede the disorder in 35% of cases.
Myeloid sarcoma lesions are composed of immature myeloid elements and therefore represent focal accumulations of leukemic cells. In contrast to its associated entities, the lesion takes the form of a solid soft tissue mass that effaces the underlying involved tissue architecture (cf. leukemic infiltrates).
They can occur as 10:
- de novo: with no prior history of myeloproliferative and myelodysplastic disorders
- simultaneously with a myeloproliferative and myelodysplastic disorder: concomitant peripheral blood and marrow involvement
- as a relapse of a treated myeloproliferative and myelodysplastic disorder
- as a form of blast transformation from a prior myeloproliferative neoplasm
Extramedullary involvement is a defining feature.
Almost any tissue can be affected, with skin and bone being the commonest. They have been reported in the skull, face, orbit, and paranasal sinuses. Lesions have been reported in the tonsils, oral and nasal cavities and within the lacrimal, thyroid and salivary glands. The central nervous system can also be affected.
It can occur in association with:
- acute myeloid leukemia (AML) (most common)
- chronic myeloid leukemia (CML)
- other myeloproliferative disorders such as
As described in the World Health Organization classification, myeloid sarcoma is considered a unique presentation and not a subtype of AML 9.
Exact imaging features will depend on the location and involved organ. Please refer to:
- CNS manifestations of granulocytic sarcoma
- spinal manifestations of granulocytic sarcoma - see article: spinal leukemia
- head and neck manifestations of granulocytic sarcoma
- skeletal manifestations of granulocytic sarcoma
- abdominal manifestations of granulocytic sarcoma
- thoracic manifestation of granulocytic sarcoma
History and etymology
- first described by A Burns in 1811 3
- termed "chloroma" in 1853 by King due to typical forms have a green color from high levels of myeloperoxidase in immature cells
- renamed as "granulocytic sarcoma" in 1966 by Rappaport when it was demonstrated that an estimated 30% of cells do not contain myeloperoxidase, therefore, a significant proportion of cells are not green in color
- recently preferred to be termed "myeloid sarcoma" 9, as several associated types of myeloid leukemia are defined by little to no granulocytic differentiation
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