Extramedullary AML

Today we discussed a case of a young man admitted with nausea, vomiting, confusion, constipation, weakness in a background of 2 months of progressive right hip pain, found to have calcium of nearly 15, creatinine ~3, hyperuricemia to 11, elevated LDH ~500, and leukocytosis to 15 but otherwise CBC normal. PET/CT with multiple FDG avid areas in bone (bilateral humerus, femurs, ribs), nondisplaced right femoral neck fracture, multiple rib fractures, and posterior neck soft tissue mass. Bone marrow biopsy with hypercellular marrow but non-diagnostic. CT guided biopsy of the soft tissue mass revealed myeloid sarcoma (extramedually acute myeloid leukemia). A few learning points: 

1) Myeloid sarcoma, also known as chloroma (owing to its green color attributed to the enzyme myeloperoxidase), is a pathologic diagnosis for an extramedullary proliferation of blasts of one or more of the myeloid lineages that disrupt the normal architecture of the tissue in which it is found.

2) Because of the rarity of this disorder,  the literature is mainly composed of case reports. It is reported in 2-8% of patients with AML either as a single or as a multifocal tumor. It can predate AML by months or years in approximately a quarter of cases, appear concomitantly with AML in 15-35% of cases, or occur after the diagnosis of AML in up to 50% of cases. It can also appear as an initial manifestation of relapse in a previously treated AML patient in remission.

3) Prognosis: The presence of myeloid sarcoma at diagnosis in a leukemic patient was traditionally considered to represent a marker for poor clinical outcome and shorter survival [Lan et al. 2009]. This is however has not been reproduced in further analyses. In fact, in a retrospective analysis of 1832 children, including 199 with EMD, treated within the Children's Cancer Group's chemotherapy trials, the presence of non-skin EMD was actually associated with a better outcome compared with AML patients without EMD [Dusenbery et al. 2003]. In subgroup analysis, children with an isolated EMD had a significantly better event-free survival (EFS) compared with children with EMD concurrent with AML and children with AML and no EMD.

For more information, check out this nice article summarizing what is known about myeloid sarcoma from the journal of Therapeutic Advances in Hematology (2011). 

Myeloid sarcoma in bone. The freshly cut surface of these tumors often has a green tint due to high myeloperoxidase content of immature myeloid cells, hence they were referred to as Chloroma.

Myeloid sarcoma in bone. The freshly cut surface of these tumors often has a green tint due to high myeloperoxidase content of immature myeloid cells, hence they were referred to as Chloroma.