Cancer is a term used for diseases where abnormal cells divide without control and are able to invade other tissues. Cancer is not just one disease, but many diseases. There are more than 100 different types of cancer.
Leukemia is one type of cancer. Review the FAQs below for more information about leukemia.
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Leukemia is cancer that starts in the tissue that forms blood. In a person with leukemia, the bone marrow makes abnormal white blood cells. The abnormal cells are leukemia cells. Unlike normal blood cells, leukemia cells don't die when they should. They may crowd out normal white blood cells, red blood cells, and platelets. This makes it hard for normal blood cells to do their work.
There are four common types of leukemia:
- Chronic lymphocytic leukemia (CLL): CLL usually grows slowly. It accounts for more than 15,000 new cases of leukemia each year. Most often, people diagnosed with the disease are over age 55. It almost never affects children.
- Chronic myeloid leukemia (CML): CML usually grows slowly at first. It accounts for nearly 5,000 new cases of leukemia each year. It mainly affects adults.
- Acute lymphocytic (lymphoblastic) leukemia (ALL): ALL grows quickly. It accounts for more than 5,000 new cases of leukemia each year. ALL is the most common type of leukemia in young children. It also affects adults.
- Acute myeloid leukemia (AML): AML grows quickly. It accounts for more than 13,000 new cases of leukemia each year. It occurs in both adults and children.
There are risk factors that increase the chance of developing leukemia, but they may differ for the different types of leukemia:
- Smoking. Smoking cigarettes increases the risk of acute myeloid leukemia.
- Benzene. Exposure to benzene in the workplace can cause acute myeloid leukemia. It may also cause chronic myeloid leukemia or acute lymphocytic leukemia. Benzene is used widely in the chemical industry. It's also found in cigarette smoke and gasoline.
- Chemotherapy. Cancer patients treated with certain types of cancer-fighting drugs sometimes later get acute myeloid leukemia or acute lymphocytic leukemia. For example, being treated with drugs known as alkylating agents or topoisomerase inhibitors is linked with a small chance of later developing acute leukemia.
- Down syndrome. Down syndrome and certain other inherited diseases increase the risk of developing acute leukemia.
- Myelodysplastic syndrome and certain other blood disorders. People with certain blood disorders are at increased risk of acute myeloid leukemia.
- Human T-cell leukemia virus type I (HTLV-I). People with HTLV-I infection are at increased risk of a rare type of leukemia known as adult T-cell leukemia. Although the HTLV-I virus may cause this rare disease, adult T-cell leukemia and other types of leukemia are not contagious.
- Family history of leukemia. It's rare for more than one person in a family to have leukemia. When it does happen, it's most likely to involve chronic lymphocytic leukemia. However, only a few people with chronic lymphocytic leukemia have a father, mother, brother, sister, or child who also has the disease.
- Open Radiation. People exposed to very high levels of radiation are much more likely than others to get acute myeloid leukemia, chronic myeloid leukemia, or acute lymphocytic leukemia
Having one or more risk factors does not mean that a person will get leukemia. Most people who have risk factors never develop the disease.
- Sex. Overall, males are more likely to develop ALL than females.
- Age. Most new cases happen in children between the ages of 2 and 5 years.
- Race. White children are almost two times more likely to develop ALL than black children.
- Socioeconomic status (SES). Children with a higher SES have an increased risk for ALL.
- Ionizing radiation. Exposure to ionizing radiation increases risk for ALL.
- Genetic conditions. Children with Down syndrome, neurofibromatosis, Shwachman syndrome, Bloom syndrome, ataxia telangiectasia, Langerhans cell histiocytosis, and Klinefelter syndrome are at increased risk for ALL.
- Race. Hispanic children are at highest risk.
- Chemotherapy. Children who are exposed to alkylating agents or epipodophyllotoxins during chemotherapy treatment are at increased risk.
- Genetic conditions. Children with Down syndrome, neurofibromatosis, Shwachman syndrome, Bloom syndrome, familial monosomy 7, Kostmann granulocytopenia, and Fanconi anemia are at increased risk for AML.
A number of other factors have been investigated to determine their relationship with ALL and AML but any evidence has been inconsistent and limited. These factors include exposures to specific chemicals, paternal occupation, paternal smoking, maternal alcohol use, and factors related to birth.
International variation in the occurrence of childhood leukemias, as well as studies finding increases in risk with population growth due to migration, have lead to the theory that an infectious agent may play a role; however, studies have not been able to confirm the presence of an infectious agent.
Older age can affect the risk of developing chronic lymphocytic leukemia. Other risk factors include:
- Being middle-aged or older, male, or white
- A family history of chronic lymphocytic leukemia or cancer of the lymph system
- Having relatives who are Russian Jews or Eastern European Jews
Additional research is needed to better understand the relationship between leukemias and the environment. Risk factors vary for adults and children, and they also differ based on the type of leukemia.
For adult-onset leukemia, the most firmly established environmental risk factor is exposure to ionizing radiation, benzene, agricultural exposures, and smoking.
For acute lymphocytic leukemia in children, their exposure to ionizing radiation and a parent's exposure to pesticides and other chemicals may increase risk.