Chloromas are uncommon, localized tumor masses composed of immature white blood cells. These masses arise outside of the bone marrow and are medically termed extramedullary myeloid tumors. The presence of a chloroma is a strong indicator of an underlying systemic malignancy, most often Acute Myeloid Leukemia (AML). While rare, the diagnosis of a chloroma frequently coincides with, or sometimes precedes, the formal diagnosis of AML in the bone marrow.
What Exactly Are Chloromas?
Chloromas are dense, solid tumors consisting of immature myeloid elements, primarily myeloblasts. These myeloblasts are the cancerous precursors to white blood cells. The medical community often refers to these tumors as myeloid sarcomas or extramedullary myeloid tumors.
The name “chloroma” comes from the Greek word for green, “chloros,” describing the color of the mass upon cross-sectioning. This striking green hue results from the high concentration of the enzyme myeloperoxidase (MPO) within the immature leukemic cells. Myeloid sarcomas are considered an extramedullary presentation of systemic disease, most commonly Acute Myeloid Leukemia (AML).
The cellular composition of a chloroma is essentially the same as the leukemic cells found in the bone marrow of an AML patient. These tumors form when myeloblasts spill out of the marrow and infiltrate other organs and soft tissues. Although most cases are associated with a known AML diagnosis, a chloroma can occasionally appear as the first sign of disease. This precursor presentation sometimes occurs months before the leukemia is detectable in the blood or bone marrow, requiring immediate and thorough evaluation.
Clinical Presentation and Common Sites
Symptoms caused by a chloroma depend entirely on the anatomical site where the tumor mass develops. These tumors can appear in almost any organ or tissue, but they show a predilection for certain locations. The most frequently involved sites include bone, soft tissues, lymph nodes, the skin, and the orbit of the eye.
In the orbit, a chloroma can lead to proptosis (bulging of the eye) or cause vision changes due to the mass effect behind the eyeball. When chloromas infiltrate the skin, the condition is known as leukemia cutis, often presenting as firm, raised nodules or plaques. Involvement of the spinal canal is a particularly serious presentation, as the mass can compress the spinal cord or nerve roots. This compression potentially causes severe back pain, numbness, weakness, or a medical emergency like cauda equina syndrome.
Other common sites include the gastrointestinal tract, breast, and testes. Symptoms can range from being completely absent, with the mass found incidentally, to causing significant pain or organ dysfunction. For example, chloromas in the gums can cause gingival hypertrophy, resulting in swollen gums that bleed easily. Due to this wide range of possible locations and symptoms, a chloroma can easily be misdiagnosed as a benign mass, an infection, or a different type of tumor.
Diagnostic Procedures
Confirming the presence of a chloroma requires a multi-step diagnostic approach, beginning with imaging to locate the mass and assess its extent. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans are routinely used to visualize the tumor, especially for masses in the spine or cranium where MRI offers superior detail. Positron Emission Tomography (PET) scans can also be used to identify metabolically active lesions throughout the body and help guide the subsequent biopsy.
The definitive diagnosis relies on obtaining a tissue sample through a biopsy of the mass. Pathologists then examine the sample to confirm the presence of immature myeloid cells, or myeloblasts. Immunohistochemistry (IHC) staining is a crucial part of this process, using specific antibodies to confirm the myeloid lineage of the cells. The cells will typically stain positive for myeloid markers such as Myeloperoxidase (MPO), CD33, and CD117.
Once a chloroma is confirmed, a bone marrow biopsy and aspiration are necessary to determine if the systemic disease, AML, is already present in the marrow. Even if the bone marrow initially appears clear, the presence of the chloroma is considered a sign of systemic disease that is highly likely to progress to full-blown AML within a short period. This comprehensive evaluation ensures that the treatment plan addresses both the localized tumor and the underlying blood cancer.
Treatment Strategies and Management
The management of a chloroma is fundamentally linked to the treatment of the associated underlying systemic malignancy. Since the tumor is a manifestation of AML, the primary treatment strategy is aggressive systemic chemotherapy, following protocols designed for acute myeloid leukemia. This typically involves induction regimens that include agents like cytarabine combined with an anthracycline. The goal of chemotherapy is to eradicate the leukemic cells throughout the entire body, including the localized tumor mass.
Localized radiation therapy (RT) plays a significant supporting role, particularly for rapid symptom relief or in cases where the tumor poses an immediate threat to vital structures. A chloroma causing spinal cord compression or severe orbital involvement, for example, is often treated with RT to quickly shrink the mass and prevent irreversible damage. Low-dose radiation, typically around 20 to 24 Gray (Gy), is highly effective for achieving local control and palliation, often providing excellent symptomatic improvement in a short timeframe.
For patients who respond well to initial treatment, hematopoietic stem cell transplantation (HSCT), often referred to as a bone marrow transplant, may be considered as a consolidation therapy. HSCT is a powerful tool used to reduce the risk of relapse for the systemic AML, thereby offering the best chance for long-term remission. While the chloroma itself is often highly sensitive to both chemotherapy and radiation, the overall prognosis is ultimately dictated by the course and management of the underlying acute myeloid leukemia.