Acute granulocytic-monocytic leukemia is classified as AML-M4 in the FAB classification of acute leukemia, which is an acute leukemia in which both the granulocytic and monocytic lineages are malignantly proliferating. The patient’s bone marrow has significant nucleated cell proliferation, and the leukemic cell morphology is highly variable, with four subtypes, M4a, M4b, M4c, and M4Eo, depending on the degree of proliferation of both granulocyte and monocyte lineages.
AML-M4 is more prone to extramedullary invasion than other types of leukemia, and clinical features include:
- Gingival swelling, ulceration, necrosis, and erosions of the mouth and throat are common;
- Rash, skin lesions, and enlarged cervical lymph nodes are more prominent, and hepatosplenomegaly is more common and more pronounced than in acute granulocytic leukemia;
- Central nervous system leukemia is more common.
Total leukocyte count is elevated in most patients, with large numbers of promonocytes, more mature-appearing young monocytes, and monocytes in the blood, and elevated lysozyme in plasma and urine in most patients.
inv(16) (inter-arm inversion of chromosome 16) is seen in approximately 25% of patients with AML-M4 and results from a fusion of the MYH11 gene in the long arm with the CBFβ gene in the short arm, producing a CBFβ-MYHll fusion gene.
There are often significant bone marrow eosinophil abnormalities, either increased numbers of eosinophils or abnormal morphology of eosinophils, and most cases are thought to be of the M4Eo subtype.
The current mainstay of treatment for acute granulocytic leukemia is still chemotherapy, and the most widely used chemotherapy regimen is that of an anthracycline (erythromycin or desoxorubicin) combined with cytarabine. Allogeneic hematopoietic stem cell transplantation may be considered in young patients after the disease has achieved remission.
The prognosis for AML-M4 patients with inv(16) is good, although genetics is only one indicator of prognosis, and a good prognosis means a better outcome after receiving regular treatment, but it does not mean that no treatment is needed.