A myeloid sarcoma (chloroma, granulocytic sarcoma,: 744  extramedullary myeloid tumor) is a solid tumor composed of immature white blood cells called myeloblasts. A chloroma is an extramedullary manifestation of acute myeloid leukemia; in other words, it is a solid collection of leukemic cells occurring outside of the bone marrow. Types
In acute leukemia
Chloromas are rare; exact estimates of their prevalence are lacking, but they are uncommonly seen even by physicians specializing in the treatment of leukemia. Chloromas may be somewhat more common in patients with the following disease features:
French–American–British (FAB) classification class M2
WHO Classification (2016 revision) is a separate entity under the "Acute myeloid leukemia (AML) and related neoplasms"
those with specific cytogenetic abnormalities (e.g. t(8;21) or inv(16))
those whose myeloblasts express T-cell surface markers, CD13, or CD14
those with high peripheral white blood cell countsHowever, even in patients with the above risk factors, chloroma remains an uncommon complication of acute myeloid leukemia. Rarely, a chloroma can develop as the sole manifestation of relapse after apparently successful treatment of acute myeloid leukemia. In keeping with the general behavior of chloromas, such an event must be regarded as an early herald of a systemic relapse, rather than as a localized process. In one review of 24 patients who developed isolated chloromas after treatment for acute myeloid leukemia, the mean interval until bone marrow relapse was 7 months (range, 1 to 19 months). In myeloproliferative or myelodysplastic syndromes
Chloromas may occur in patients with a diagnosis of myelodysplastic syndrome (MDS) or myeloproliferative syndromes (MPS) (e.g.
Skin involvement typically appears as violaceous, raised, nontender plaques or nodules, which on biopsy are found to be infiltrated with myeloblasts Note that leukemia cutis differs from Sweets syndrome, in which the skin is infiltrated by mature neutrophils in a paraneoplastic process. Gum involvement (gingival hypertrophy) leads to swollen, sometimes painful gums which bleed easily with tooth brushing and other minor trauma. Other tissues which can be involved include lymph nodes, the small intestine, the mediastinum, the lung, epidural sites, the uterus, the ovaries, and the orbit of the eye. Symptoms of chloroma at these sites are related to their anatomic location; chloromas may also be asymptomatic and be discovered incidentally in the course of evaluation of a person with acute myeloid leukemia. Central nervous system involvement, as described above, most often takes the form of meningeal leukemia, or invasion of the subarachnoid space by leukemic cells. This condition is usually considered separately from chloroma, as it requires different treatment modalities. True chloromas (i.e. solid leukemic tumors) of the central nervous system are exceedingly rare, but have been described. Diagnosis
Definitive diagnosis of a chloroma usually requires a biopsy of the lesion in question. Historically, even with a tissue biopsy, pathologic misdiagnosis was an important problem, particularly in patients without a clear pre-existing diagnosis of acute myeloid leukemia to guide the pathologist.