Myeloid sarcoma is a rare tumor composed of immature myeloid cells, a type of white blood cell that originates in the bone marrow. These tumors are an extramedullary manifestation of acute myeloid leukemia (AML), meaning they are a solid collection of leukemic cells found outside the bone marrow. It has also been known as granulocytic sarcoma and chloroma, a term reflecting that the tumors can have a green color from the enzyme myeloperoxidase.
The World Health Organization recognizes this condition as a distinct presentation of AML. It is a focal mass of leukemic cells that invades and disrupts the structure of the tissue it occupies. Myeloid sarcoma can develop in individuals with no prior history of blood disorders, appear concurrently with a myeloid disorder, or signal a relapse of a previously treated condition.
Symptoms and Common Locations
The signs of myeloid sarcoma are linked to the tumor’s size and location, leading to a wide variety of symptoms. Because the tumor can arise in almost any tissue, its presentation differs greatly from one person to another. A mass may be discovered incidentally during an evaluation for a related condition like AML.
When myeloid sarcoma affects the skin, it often appears as one or more raised nodules or thicker, flat-topped plaques. These skin lesions can vary in color, presenting as reddish-brown, purple, or green. This skin involvement is sometimes called leukemia cutis.
Another common site is the lymph nodes, where the sarcoma can cause painless swelling in areas like the neck, armpits, or groin. Infiltration of bone is also frequent, which can lead to localized pain or, in some cases, weaken the bone enough to cause a fracture.
The gastrointestinal tract is another location where these tumors can form, potentially causing abdominal pain, bleeding, or a blockage. Less commonly, myeloid sarcoma can develop in other parts of the body, such as the central nervous system, causing headaches or neurological deficits. Tumors can also form in the orbits of the eyes or within breast tissue.
Diagnosis and Confirmation
Diagnosing myeloid sarcoma begins with a physical examination and a review of the patient’s medical history. If a tumor is suspected, imaging studies are performed to determine its location, size, and relationship to surrounding structures. Imaging like computed tomography (CT), magnetic resonance imaging (MRI), or PET scans are used to visualize the mass.
While imaging can identify the tumor, a diagnosis can only be confirmed through a biopsy. This procedure involves removing a small tumor sample for analysis by a pathologist.
To confirm the cells are of myeloid origin, a specialized staining technique called immunohistochemistry is used. This method uses antibodies to detect specific protein markers on the cell surface. The presence of myeloid markers like myeloperoxidase (MPO), CD33, or lysozyme confirms the diagnosis and distinguishes it from other cancers like lymphoma.
Once myeloid sarcoma is confirmed, evaluating the bone marrow is a standard next step. A bone marrow aspirate and biopsy are performed to check for an underlying systemic disease like acute myeloid leukemia (AML) or a myelodysplastic syndrome (MDS). This evaluation is important for understanding the full extent of the disease and guiding treatment decisions.
Treatment Approaches
The primary treatment for myeloid sarcoma is systemic chemotherapy, similar to regimens used for acute myeloid leukemia (AML). This approach is recommended even when the sarcoma appears isolated, as it is often a manifestation of a systemic disease. Chemotherapy eliminates cancer cells that may be circulating or undetected in the bone marrow. Standard induction regimens often include drugs like cytarabine combined with an anthracycline.
Radiation therapy is an effective tool for local control of the tumor. It can be used to shrink masses that are causing symptoms, such as pain or pressure on an organ. Radiation may also be used to treat any residual disease after chemotherapy, helping to reduce the risk of the tumor recurring in the same location.
For eligible patients, a hematopoietic stem cell transplant (HSCT) may be considered. This procedure is often for individuals with an associated bone marrow disease or a higher risk of relapse. The goal of a stem cell transplant is to replace the patient’s diseased hematopoietic system with a healthy one, offering the potential for a long-term cure.
The role of surgery in managing myeloid sarcoma is limited. While not a primary treatment, it is used to obtain the biopsy for diagnosis. In rare situations, surgery might be performed to relieve an obstruction caused by the tumor, such as in the gastrointestinal tract. Researchers are also investigating targeted therapies that focus on specific genetic mutations.
Prognosis and Associated Conditions
The long-term outlook for myeloid sarcoma is not determined by the tumor’s size or location. The primary factor influencing prognosis is the status of the bone marrow. The presence or absence of an underlying systemic myeloid disease, such as acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS), largely shapes the expected outcome.
When an isolated myeloid sarcoma is found with no evidence of bone marrow disease, the prognosis is more favorable. However, there remains a high likelihood of developing AML later. This is why systemic chemotherapy is the standard of care even in these cases.
When the sarcoma is diagnosed at the same time as an established bone marrow disorder like AML or MDS, the prognosis is tied to that condition’s specific characteristics. The disease is managed according to the protocols for that primary disorder.
The prognosis is more challenging when a myeloid sarcoma appears as a sign of relapse in a patient previously treated for a myeloid disorder. The sarcoma’s appearance indicates the original disease has returned. Additionally, specific genetic mutations found within the tumor cells can provide further prognostic information and may help guide treatment.