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Chloroma

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chloroma myeloid sarcoma

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Chloroma (Granulocytic Sarcoma / Myeloid Sarcoma)

Definition and Nomenclature

A chloroma is a solid, extramedullary tumor composed of immature myeloid cells (blasts). The term "chloroma" derives from the Greek word for green - fresh lesions have a characteristic greenish tint due to the high content of myeloperoxidase (MPO). This color can be enhanced by rubbing the cut surface with alcohol. Because the green color is variable and not always present, the preferred current terms are granulocytic sarcoma or myeloid sarcoma. Other historical names include myeloblastic sarcoma and extramedullary myeloid cell tumor.
  • Andrews' Diseases of the Skin, p. 3099
  • Henry's Clinical Diagnosis and Management by Laboratory Methods

Associated Conditions (Four Clinical Settings)

Chloromas occur in four distinct contexts:
  1. Known AML - the most common association; occurs in ~3% of patients with myelogenous leukemia
  2. CML or MDS - as a harbinger of an impending blast crisis
  3. De novo presentation - in a previously undiagnosed patient, as the first sign of AML
  4. Post-bone marrow transplantation (BMT) - as the initial sign of relapse
Rarely, a chloroma can precede systemic leukemia, which makes the diagnosis particularly challenging, especially when biopsy mistakenly suggests a lymphoma or solid tumor.
  • Andrews' Diseases of the Skin, p. 3097
  • Henry's Clinical Diagnosis and Management by Laboratory Methods

Epidemiology

  • Incidence: 2.5-9.1% of AML cases on imaging series
  • Orbital myeloid sarcoma in children typically presents around age 7 years
  • AML overall has a median age of 65 years, but chloromas can occur at any age

Sites of Involvement

Chloromas can arise at virtually any extramedullary site:
Site CategoryExamples
Bone / PeriosteumSkull, spine, ribs, sternum (most common on imaging)
Soft tissueSubcutaneous nodules
Skin20-50% of reported cases
Orbit / EyeRapid-onset proptosis, bilateral, lid edema, ecchymosis
ENT / Head & NeckTemporal bone, nasopharynx, upper respiratory tract
Lymph nodes-
VisceraBreast, ovary, perineural/epidural structures
PleuraPleural thickening mimicking pleural effusion
  • Cummings Otolaryngology Head and Neck Surgery
  • Kanski's Clinical Ophthalmology, p. 6782
  • Grainger & Allison's Diagnostic Radiology

Skin Lesions

Cutaneous chloromas (leukemia cutis) appear as:
  • Red, mahogany, or violaceous firm nodules
  • Predilection for the face, scalp, and trunk
  • May be solitary or multiple
The green tint typical of fresh lesions is due to myeloperoxidase and can be enhanced by alcohol.

Microscopy and Pathology

AML blast morphology: peripheral blood smears (a-e) show myeloblasts with nuclear complexity, granules, and vacuoles compared to lymphoblasts; (f) bone marrow biopsy section showing sheets of blasts
AML / myeloblast morphology - Quick Compendium of Clinical Pathology, 5th ed.
Key morphologic features:
  • Myeloblasts have more nuclear complexity and more cytoplasm (with granules and vacuoles) compared to lymphoblasts
  • Auer rods - pathognomonic needle-like cytoplasmic inclusions; the only specific morphologic finding in AML
  • Sheets of immature cells infiltrating extramedullary tissue

Diagnostic Pitfalls

Chloromas are frequently misdiagnosed as:
  • Non-Hodgkin lymphoma (most common error)
  • Amelanotic melanoma
  • Undifferentiated carcinoma
To avoid misdiagnosis: make touch imprint preparations from cut sections and stain with Romanowsky stains; perform cytochemistry and immunophenotyping.

Immunophenotyping

Key markers:
  • Anti-MPO (myeloperoxidase) - granulocytic lineage
  • CD68 - monocytic lineage
  • HLA-DR - positive in most AML subtypes (exception: acute promyelocytic leukemia/APL is HLA-DR negative)
  • CD13, CD33 - myeloid markers
  • CD19 - typically negative (anomalous expression in AML with t(8;21))

Radiology (MRI Features)

  • Chloroma manifests as an extra-osseous mass:
    • Isointense to muscle on T1-weighted sequences
    • Hyperintense to muscle on PD-weighted / T2-weighted sequences
    • Avid enhancement following contrast administration
  • Most common skeletal locations in children: skull, spine, ribs, sternum
  • Pattern can mimic Ewing sarcoma (diffuse, permeative bone destruction)
  • FDG-PET shows focal/diffuse increased uptake
  • Grainger & Allison's Diagnostic Radiology

CML Blast Crisis Context

In CML, a tissue infiltrate of blasts (chloroma) is one of the criteria for declaring blast phase:
  • 20% blasts in blood or marrow, OR
  • A tissue infiltrate of blasts (chloroma), OR
  • Prominent focal accumulation of blasts in the marrow biopsy
  • Quick Compendium of Clinical Pathology, 5th ed.

Management

  • Local irradiation for symptomatic/localized disease
  • Systemic chemotherapy as for AML (the diagnosis of a chloroma is considered equivalent to AML)
  • Bone marrow transplantation is the definitive treatment for eligible patients
  • Marrow involvement usually follows if not already antecedent - patients with de novo chloroma must be treated systemically

Recent Evidence

A 2025 meta-analysis (PMID 40558061) examined the prognostic impact of extramedullary disease (including chloroma/myeloid sarcoma) in AML and found that extramedullary involvement is a significant negative prognostic factor in AML. This is consistent with the textbook teaching that a chloroma has the same clinical gravity as systemic AML.
Summary: Chloroma = myeloid sarcoma = granulocytic sarcoma. It is an extramedullary deposit of myeloid blasts, most often tied to AML (or CML/MDS in blast crisis), green due to myeloperoxidase, occurring at diverse sites (skin, orbit, bone, soft tissue), frequently misdiagnosed as lymphoma on histology, and treated as systemic AML with chemotherapy ± radiation.
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