Leukemia is a cancer of the blood cells. There are several broad categories of blood cells, including red blood cells (RBCs), white blood cells (WBCs), and platelets. Generally, leukemia refers to cancers of the WBCs.
WBCs are a vital part of your immune system. They protect your body from invasion by bacteria, viruses, and fungi, as well as from abnormal cells and other foreign substances. In leukemia, the WBCs don’t function like normal WBCs. They can also divide too quickly and eventually crowd out normal cells.
WBCs are mostly produced in the bone marrow, but certain types of WBCs are also made in the lymph nodes, spleen, and thymus gland. Once formed, WBCs circulate throughout your body in your blood and lymph (fluid that circulates through the lymphatic system), concentrating in the lymph nodes and spleen.
Risk factors for leukemia
The causes of leukemia aren’t known. However, several factors have been identified which may increase your risk. These include:
• a family history of leukemia
• smoking, which increases your risk of developing acute myeloid leukemia (AML)
• genetic disorders such as Down syndrome
• blood disorders, such as myelodysplastic syndrome, which is sometimes called “preleukemia”
• previous treatment for cancer with chemotherapy or radiation
• exposure to high levels of radiation
• exposure to chemicals such as benzene
The types of leukemia
The onset of leukemia can be acute (sudden onset) or chronic (slow onset). In acute leukemia, cancer cells multiply quickly. In chronic leukemia, the disease progresses slowly and early symptoms may be very mild.
Leukemia is also classified according to the type of cell. Leukemia involving myeloid cells is called myelogenous leukemia. Myeloid cells are immature blood cells that’d normally become granulocytes or monocytes. Leukemia involving lymphocytes is called lymphocytic leukemia. There are four main types of leukemia:
Acute myelogenous leukemia (AML)
Acute myelogenous leukemia (AML) can occur in children and adults. According to the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute (NCI), about 21,000 new cases of AML are diagnosed annually in the United States. This is the most common form of leukemia. The five-year survival rate for AML is 26.9 percent.
Acute lymphocytic leukemia (ALL)
Acute lymphocytic leukemia (ALL) occurs mostly in children. The NCI estimates about 6,000 new cases of ALL are diagnosed annually. The five-year survival rate for ALL is 68.2 percent.
Chronic myelogenous leukemia (CML)
Chronic myelogenous leukemia (CML) affects mostly adults. About 9,000 new cases of CML are diagnosed annually, according to the NCI. The five-year survival rate for CML is 66.9 percent.
Chronic lymphocytic leukemia (CLL)
Chronic lymphocytic leukemia (CLL) is most likely to affect people over the age of 55. It’s very rarely seen in children. According to the NCI, about 20,000 new cases of CLL are diagnosed annually. The five-year survival rate for CLL is 83.2 percent.
Hairy cell leukemia is a very rare subtype of CLL. Its name comes from the appearance of the cancerous lymphocytes under a microscope.
What are the symptoms of leukemia?
The symptoms of leukemia include:
• excessive sweating, especially at night (called “night sweats”)
• fatigue and weakness that don’t go away with rest
• unintentional weight loss
• bone pain and tenderness
• painless, swollen lymph nodes (especially in the neck and armpits)
• enlargement of the liver or spleen
• red spots on the skin, called petechiae
• bleeding easily and bruising easily
• fever or chills
• frequent infections
Leukemia can also cause symptoms in organs that have been infiltrated or affected by the cancer cells. For example, if the cancer spreads to the central nervous system, it can cause headaches, nausea and vomiting, confusion, loss of muscle control, and seizures.
Leukemia can also spread to other parts of your body, including:
• the lungs
• gastrointestinal tract
Leukemia may be suspected if you have certain risk factors or concerning symptoms. Your doctor will begin with a complete history and physical examination, but leukemia can’t be fully diagnosed by a physical exam. Instead, doctors will use blood tests, biopsies, and imaging tests to make a diagnosis.
There are a number of different tests that can be used to diagnose leukemia. A complete blood count determines the numbers of RBCs, WBCs, and platelets in the blood. Looking at your blood under a microscope can also determine if the cells have an abnormal appearance.
Tissue biopsiescan be taken from the bone marrow or lymph nodes to look for evidence of leukemia. These small samples can identify the type of leukemia and its growth rate. Biopsies of other organs such as the liver and spleen can show if the cancer has spread.
Once leukemia is diagnosed, it’ll be staged. Staging helps your doctor determine your outlook.
AML and ALL are staged based on how cancer cells look under the microscope and the type of cell involved. ALL and CLL are staged based on the WBC count at the time of diagnosis. The presence of immature white blood cells, or myeloblasts, in the blood and bone marrow is also used to stage AML and CML.
Assessing the progression
A number of other tests can be used to assess the progression of the disease:
• Flow cytometry examines the DNA of the cancer cells and determines their growth rate.
• Liver function tests show whether leukemia cells are affecting or invading the liver.
• Lumbar puncture is performed by inserting a thin needle between the vertebrae of your lower back. This allows your doctor to collect spinal fluid and determine if the cancer has spread to the central nervous system.
• Imaging tests, such as X-rays, ultrasounds, and CT scans, help doctors look for any damage to other organs that’s caused by the leukemia.
Leukemia is usually treated by a hematologist-oncologist. These are doctors who specialize in blood disorders and cancer. The treatment depends on the type and stage of the cancer. Some forms of leukemia grow slowly and don’t need immediate treatment. However, treatment for leukemia usually involves one or more of the following:
• Chemotherapy uses drugs to kill leukemia cells. Depending on the type of leukemia, you may take either a single drug or a combination of different drugs.
• Radiation therapy uses high-energy radiation to damage leukemia cells and inhibit their growth. Radiation can be applied to a specific area or to your entire body.
• Stem cell transplantation replaces diseased bone marrow with healthy bone marrow, either your own (called autologous transplantation) or from a donor (called allologous transplantation). This procedure is also called a bone marrow transplant.
• Biological or immune therapy uses treatments that help your immune system recognize and attack cancer cells.
• Targeted therapy uses medications that take advantage of vulnerabilities in cancer cells. For example, imatinib (Gleevec) is a targeted drug that’s commonly used against CML.