Myeloid cancer is a group of cancers that begin in the blood-forming myeloid stem cells of the bone marrow. Normally, these cells mature into red blood cells that carry oxygen, platelets that help form clots, and various types of white blood cells that fight infection.
The primary issue in myeloid cancers is a disruption of this maturation process. Genetic mutations cause a myeloid cell to multiply uncontrollably, producing abnormal, immature cells called blasts. These cancerous cells build up in the bone marrow and blood, crowding out healthy cells and leading to the signs and symptoms of the disease.
Types of Myeloid Cancer
Myeloid cancer is not a single disease but an umbrella term for several distinct conditions. These cancers are broadly classified based on how quickly they progress and the maturity of the cancerous cells.
Acute Myeloid Leukemia (AML) is a common type characterized by rapid progression. The bone marrow produces a high number of immature white blood cells called myeloblasts. These abnormal cells do not develop into healthy white blood cells, and their accumulation leads to a swift onset of symptoms.
Chronic Myeloid Leukemia (CML) is a slower-progressing disease defined by the overproduction of more developed, but still abnormal, granulocytes. Although these cells are more mature than the blasts in AML, they do not function properly. The progression of CML is gradual, and some individuals may not experience symptoms in the early stages.
Myelodysplastic Syndromes (MDS) are disorders where the bone marrow fails to produce enough healthy, mature blood cells. The marrow creates defective, abnormal-looking cells that often die before entering the bloodstream. This results in low counts of one or more blood cell types, a condition known as cytopenia.
Myeloproliferative Neoplasms (MPNs) involve the overproduction of mature, functioning blood cells. Unlike MDS, MPNs are defined by excessive production. Examples include polycythemia vera (too many red blood cells) and essential thrombocythemia (excess platelets). Although these cells are mature, their high numbers can cause complications.
Common Symptoms and Signs
The symptoms of myeloid cancers are a direct result of the bone marrow’s inability to produce sufficient numbers of healthy blood cells. Because red blood cells, white blood cells, and platelets are all affected, the signs can be widespread and varied.
A shortage of red blood cells (anemia) is a frequent finding. This leads to persistent fatigue, weakness, shortness of breath during routine activities, and pale skin. Dizziness and feeling cold may also occur as the body’s tissues are deprived of adequate oxygen.
Impaired production of functional white blood cells (neutropenia) makes the body vulnerable to infections. Individuals may experience fevers, frequent illnesses that are difficult to resolve, or sores that do not heal properly.
A low platelet count (thrombocytopenia) interferes with the blood’s ability to clot. This can manifest as easy bruising, frequent nosebleeds, and bleeding from the gums. Some people may notice tiny, pinpoint red spots on their skin, called petechiae, which are caused by minor bleeding under the skin. Other general symptoms can include unexplained weight loss, loss of appetite, night sweats, and pain in the bones or joints.
Risk Factors and Potential Causes
While the exact cause of any single case of myeloid cancer is often not identified, researchers have found several factors that can increase a person’s risk.
Age is a significant risk factor, as the likelihood of a myeloid cancer diagnosis increases after age 60. Prior cancer treatment is another established risk. Exposure to certain chemotherapy drugs or radiation therapy can damage bone marrow cell DNA, sometimes leading to a secondary cancer.
Certain genetic syndromes, such as Down syndrome and Fanconi anemia, carry a greater risk of developing acute leukemia. Long-term exposure to industrial chemicals like benzene is also a known risk factor for AML. Since benzene is found in cigarette smoke, smoking is directly linked to an increased risk.
Individuals with a pre-existing blood disorder, such as MDS or an MPN, have a recognized risk of their condition transforming into AML. The initial disorder represents a state of instability in the bone marrow, which can progress to a more aggressive cancer.
The Diagnostic Process
The diagnostic process begins with a physical exam, where a doctor checks for signs like pale skin, swollen lymph nodes, or an enlarged liver or spleen.
The first investigative step is a complete blood count (CBC) with differential. This blood test measures the quantities and appearance of red blood cells, white blood cells, and platelets. Abnormal counts or the presence of blast cells are strong indicators of a myeloid disorder.
If blood tests are abnormal, the primary diagnostic procedure is a bone marrow aspiration and biopsy. This involves taking small samples of liquid marrow and bone from the hip bone. These samples are sent to a laboratory where a pathologist examines them to confirm the presence of cancer, determine the percentage of blast cells, and assess marrow health.
Specialized laboratory tests on the bone marrow or blood samples help refine the diagnosis and guide treatment. Cytogenetic analysis looks for changes in the cancer cell chromosomes, such as the Philadelphia chromosome found in CML. Molecular testing searches for specific gene mutations to provide prognostic information and identify targets for therapy.
Treatment Approaches
Treatment for myeloid cancer depends on the specific type, the patient’s age and health, and the cancer’s genetic features. The primary goal is to eliminate cancerous cells and restore normal bone marrow function. Treatment plans are often multi-faceted and may evolve.
Chemotherapy is a common treatment for many myeloid cancers, especially acute forms like AML. It uses powerful drugs to kill rapidly dividing cells. Treatment is often administered in phases, starting with an “induction” phase to achieve remission, followed by a “consolidation” phase to eliminate remaining cancer cells.
Targeted therapy uses drugs designed to attack specific vulnerabilities in cancer cells, often targeting the products of genetic mutations. For example, tyrosine kinase inhibitors (TKIs) are highly effective in treating CML. They work by blocking the protein produced by the Philadelphia chromosome.
A stem cell transplant, or bone marrow transplant, may be an option for some patients. This procedure replaces the patient’s diseased bone marrow with healthy blood-forming stem cells from a matched donor. It is an intensive treatment reserved for younger, healthier patients with high-risk disease, as it involves high-dose chemotherapy or radiation to first eliminate the existing bone marrow.
Supportive care is a component of nearly every treatment plan to manage symptoms and side effects. Common strategies include blood and platelet transfusions to address low counts. Antibiotics are used to treat or prevent infections, and other medications can stimulate healthy blood cell growth.