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Characteristics

Acute myeloid leukemia (AML) develops in the bone marrow as a result of mutations in the DNA of specific blood stem cells (myeloid cells). These myeloid cells normally develop into different types of white blood cells (e.g., neutrophils and monocytes), red blood cells, or platelets. Due to mutations these cells are no longer able to fulfill their normal function and become immature, cancerous cells referred to as myeloblasts. As a result of their uncontrolled growth, these myeloblasts fill up the bone marrow, preventing the production of normal blood cells. In addition to this, AML cells accumulate in the blood stream.

AML is a rare form of cancer, with about 300 new cases in Belgium in 2020. AML occurs in people of all ages but is most common in adults older than 65 years. For most patients with AML, the cause of their disease is unclear. However, several factors have been identified that increase the risk for AML, including exposure to chemotherapy, radiation, or specific chemicals (e.g., benzene), certain rare inherited conditions (e.g., Down’s syndrome), smoking, and the presence of other bone marrow disorders (e.g., myelofibrosis, MDS, polycythemia vera).

Symptoms

The symptoms of AML can be vague and often mimic other, less serious conditions. In general, AML symptoms develop quickly, within a couple of days or weeks. These symptoms can include a general feeling of weakness and fatigue, paleness, a high temperature, flu-like symptoms, and a tendency to easily pick up infections such as coughs or colds. Patients with AML may also be prone to bleeding (e.g., nose bleeds, bleeding gums, prolonged bleeding from minor cuts) and bruising, may have unexplained weight loss and can suffer from breathlessness and bone, back or abdominal pain. In addition, lumps caused by swollen lymph nodes can occur in the neck, armpits, abdomen, or groin.

Diagnostic tests

When AML is suspected, a blood test will be performed to measure the number of red blood cells, white blood cells and platelets. In addition, the appearance of the different blood cells under the microscope will be evaluated. Most patients with AML have an excess amount of immature white blood cells in their blood, and not enough red blood cells or platelets. While these findings may suggest AML, a definite diagnosis usually requires a bone marrow test. To this end, a bone marrow sample is removed from the hipbone or sternum (breastbone) and sent to the lab for a further evaluation of the size, shape, and molecular and genetic features of the cells in the bone marrow. These tests allow physicians to determine the exact AML subtype, which has an impact on the prognosis and the subsequent treatment plan.

Usually, leukemia does not form tumors and, as a result, medical imaging tests (X-ray, CT-scans, MRI, ultrasound) are less important in the diagnostic work-up of AML than for solid tumors. However, when the AML is suspected to have spread beyond the blood and bone marrow, imaging tests can be requested.

Treatments

AML is an aggressive disease and patients need to be treated as soon as possible after their diagnosis. The main treatment for young and fit patients with AML consists of chemotherapy, which is usually given in different phases. In the induction phase, intensive chemotherapy is given to push the leukemia into a (complete) remission. This means that leukemia cells can no longer be found in bone marrow samples. The intensity of the chemotherapy that is used is determined by the age and fitness of the patient. For patients who have a mutation in the FLT3 gene, targeted therapy can be added to the chemotherapy. The same holds true for patients having the CD33 protein on the surface of their tumor cells.

During the consolidation phase of the treatment, a second course of intensive chemotherapy is used to destroy any remaining leukemia cells in the body. For patients who received a targeted drug during induction, this is usually continued in the consolidation phase. In a proportion of patients, stem cell transplantation can be used as consolidation therapy.

For elderly, or frail patients, the intensive treatment strategy discussed above is not an option. For these patients, the treatment consists of low-dose chemotherapy with hypomethylating agents, either alone or in combination with targeted therapy.

Some patients have residual leukemia cells in their bone marrow after they receive intensive chemotherapy. In these cases, the disease is referred to as being “refractory”. Other patients may achieve remission but later experience a return of leukemia cells in their bone marrow. This is referred to as a “relapse” of the disease. For patients with relapsed/refractory AML, stem cell transplantation may be the best option. In patients who are unable to undergo a stem cell transplantation, low-dose chemotherapy alone, or in combination with targeted therapy is used. In addition, many new drugs and combinations are under evaluation in clinical trials and these studies may provide alternative treatment options.

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