Leukemia is a cancer that usually begin in the bone marrow and result in high numbers of abnormal white blood cells which are not fully developed. Symptoms may include bleeding and bruising problems, feeling tired, fever, and an increased risk of infections. These symptoms occur due to a lack of normal blood cells. Diagnosis is typically made by bone marrow biopsy.
The exact cause of leukemia is unknown. Different kinds of leukemia are believed to have different causes.
Both inherited and non-inherited are believed to be involved. Risk factors include smoking, ionizing radiation, some chemicals, and Down syndrome.
People with a family history of leukemia are also at higher risk. In children under 15, the five-year survival rate is greater than 60 to 85%, depending on the type of leukemia.
In children with acute leukemia who are cancer-free after five years, the cancer is unlikely to return.
Leukemia is cancer of white blood cells that starts in the bone marrow, the soft material in the center of bones that makes white blood cells, red blood cells and platelets.
The abnormal white blood cells in leukemia are genetically identical. They proliferate and eventually outnumber normal blood cells, interrupting their work.
"In the blood can be such a high count of white blood cells present that it can start causing problems in the circulation. In the bone marrow, the leukemic cells overtake the bone marrow and suppress the formation of the normal blood components," said Dr. Sarah Vaiselbuh, a pediatric hematologist and oncologist at Staten Island University Hospital in New York.
Children or adults are often anemic and need transfusion," Vaiselbuh said. "They have very low platelet counts and are at risk of bleeding, and most importantly, their normal blood cells are no longer produced in adequate numbers, so they can't fight infection."
About 52,400 new diagnoses of leukemia are expected in the United States in 2014, and it is estimated that about 24,000 people will die of this cancer in 2014, according to the National Cancer Institute. In 2011, there were an estimated 302,800 people living with leukemia in the United States, but new leukemia cases constitute about 3 percent of all new cancer cases each year.
In children, leukemia is the most common type of cancer, but more adults get diagnosed with leukemia, according to the Leukemia and Lymphoma Society (LLS). In 2011, about nine children per 100,000 children ages 1-4 were diagnosed with leukemia.
Survival rates for leukemia have remarkably improved over the past decades. Considering all types of leukemia in both children and adults together, in 1963, the five-year survival rate (five years after the end of treatment), was only 14 percent.
But a 2009 study has found that this survival rate is now up to 59 percent, Vaiselbuh said. The progress shows the importance of continued support for leukemia research, she said.
Types
- Acute lymphoblastic leukemia (ALL) is the most common type of leukemia in young children. It also affects adults, especially those 65 and older. Standard treatments involve chemotherapy and radiotherapy. The survival rates vary by age: 85% in children and 50% in adults. Subtypes include precursor B acute lymphoblastic leukemia, precursor T acute lymphoblastic leukemia, Burkitt's leukemia, and acute biphenotypic leukemia.
- Chronic lymphocytic leukemia (CLL) most often affects adults over the age of 55. It sometimes occurs in younger adults, but it almost never affects children. Two-thirds of affected people are men. The five-year survival rate is 75%. It is incurable, but there are many effective treatments. One subtype is B-cell prolymphocytic leukemia, a more aggressive disease.
- Acute myelogenous leukemia (AML) occurs more commonly in adults than in children, and more commonly in men than women. It is treated with chemotherapy. The five-year survival rate is 40%, except for APL (Acute Promyelocytic Leukemia), which has a survival rate greater than 90%. Subtypes of AML include acute promyelocytic leukemia, acute myeloblastic leukemia, and acute megakaryoblastic leukemia.
- Chronic myelogenous leukemia (CML) occurs mainly in adults; a very small number of children also develop this disease. It is treated with imatinib (Gleevec in United States, Glivec in Europe) or other drugs. The five-year survival rate is 90%. One subtype is chronic myelomonocytic leukemia.
- Hairy cell leukemia (HCL) is sometimes considered a subset of chronic lymphocytic leukemia, but does not fit neatly into this category. About 80% of affected people are adult men. No cases in children have been reported. HCL is incurable but easily treatable. Survival is 96% to 100% at ten years.
- T-cell prolymphocytic leukemia (T-PLL) is a very rare and aggressive leukemia affecting adults; somewhat more men than women are diagnosed with this disease. Despite its overall rarity, it is the most common type of mature T cell leukemia; nearly all other leukemias involve B cells. It is difficult to treat, and the median survival is measured in months.
- Large granular lymphocytic leukemia may involve either T-cells or NK cells; like hairy cell leukemia, which involves solely B cells, it is a rare and indolent (not aggressive) leukemia.
- Adult T-cell leukemia is caused by human T-lymphotropic virus (HTLV), a virus similar to HIV.
Like HIV, HTLV infects CD4+ T-cells and replicates within them;
however, unlike HIV, it does not destroy them. Instead, HTLV
"immortalizes" the infected T-cells, giving them the ability to
proliferate abnormally. Human T-cell lymphotropic virus types I and II
(HTLV-I/II) are endemic in certain areas of the world.
Causes
There is no single known cause for any of the different types of leukemia. The few known causes, which are not generally factors within the control of the average person, account for relatively few cases. The cause for most cases of leukemia is unknown. The different leukemias likely have different causes.
Leukemia, like other cancers, results from mutations in the DNA. Certain mutations can trigger leukemia by activating oncogenes or deactivating tumor suppressor genes, and thereby disrupting the regulation of cell death, differentiation or division. These mutations may occur spontaneously or as a result of exposure to radiation.
Among adults, the known causes are natural and artificial ionizing radiation, a few viruses such as human T-lymphotropic virus, and some chemicals, notably benzene and alkylating chemotherapy agents for previous malignancies.
Use of tobacco is associated with a small increase in the risk of developing acute myeloid leukemia in adults. Cohort and case-control studies have linked exposure to some petrochemicals and hair dyes to the development of some forms of leukemia.
Diet has very limited or no effect, although eating more vegetables may confer a small protective benefit.
Viruses have also been linked to some forms of leukemia. For example, human T-lymphotropic virus (HTLV-1) causes adult T-cell leukemia.
Some people have a genetic predisposition towards developing leukemia. This predisposition is demonstrated by family histories and twin studies.
The affected people may have a single gene or multiple genes in common. In some cases, families tend to develop the same kinds of leukemia as other members; in other families, affected people may develop different forms of leukemia or related blood cancers.
People with Down syndrome have a significantly increased risk of developing forms of acute leukemia.
Whether non-ionizing radiation causes leukemia has been studied for several decades. The International Agency for Research on Cancer expert working group undertook a detailed review of all data on static and extremely low frequency electromagnetic energy, which occurs naturally and in association with the generation, transmission, and use of electrical power.They concluded that there is limited evidence that high levels of ELF magnetic (but not electric) fields might cause some cases of childhood leukemia.
No evidence for a relationship to leukemia or another form of malignancy in adults has been demonstrated. Since exposure to such levels of ELFs is relatively uncommon, the World Health Organization concludes that ELF exposure, if later proven to be causative, would account for just 100 to 2400 cases worldwide each year, representing 0.2 to 4.9% of the total incidence of childhood leukemia for that year (about 0.03 to 0.9% of all leukemias).
A few cases of maternal-fetal transmission (a baby acquires leukemia because its mother had leukemia during the pregnancy) have been reported.
According to a study conducted at the Center for Research in Epidemiology and Population Health in France, children born to mothers who use fertility drugs to induce ovulation are more than twice as likely to develop leukemia during their childhoods than other children.
Damage to the bone marrow, by way of displacing the normal bone marrow cells with higher numbers of immature white blood cells, results in a lack of blood platelets, which are important in the blood clotting process.
This means people with leukemia may easily become bruised, bleed excessively, or develop pinprick bleeds (petechiae).
White blood cells, which are involved in fighting pathogens, may be suppressed or dysfunctional. This could cause the patient's immune system to be unable to fight off a simple infection or to start attacking other body cells. Because leukemia prevents the immune system from working normally, some patients experience frequent infection, ranging from infected tonsils, sores in the mouth, or diarrhea to life-threatening pneumonia or opportunistic infections.
Finally, the red blood cell deficiency leads to anemia, which may cause dyspnea and pallor.
Some patients experience other symptoms, such as feeling sick, having fevers, chills, night sweats, feeling fatigued and other flu-like symptoms. Some patients experience nausea or a feeling of fullness due to an enlarged liver and spleen; this can result in unintentional weight loss. Blasts affected by the disease may come together and become swollen in the liver or in the lymph nodes causing pain and leading to nausea.
If the leukemic cells invade the central nervous system, then neurological symptoms (notably headaches) can occur. Uncommon neurological symptoms like migraines, seizures, or coma can occur as a result of brain stem pressure. All symptoms associated with leukemia can be attributed to other diseases. Consequently, leukemia is always diagnosed through medical tests.
According to the LLS, common symptoms include:
- Chills, fever or night sweats
- Persistent weakness and fatigue
- Shortness of breath upon exertion
- Pale skin
- Pinhead-sized red dots under the skin
- Unexplained bruises
- Slow-healing cuts and excess bleeding
- Joint or bone aches
- Swollen lymph nodes
Treatment
Treatment for leukemia depends on the type of leukemia and other factors such as the patient's age, white blood cell count and genetics of the cancer.The main treatment is chemotherapy, which involves injecting a combination of drugs in the blood and sometimes in the spinal fluid.
If patient's cancer comes back after chemotherapy, doctors may consider bone marrow transplantation. They will screen the patient's sibling or the bone marrow register to find a donor who matches with the patient, Vaiselbuh said.
A bone marrow transplantation replaces the diseased bone marrow by the healthy bone marrow of the donor to eradicate the disease, Vaiselbuh said.
Additional treatments may involve radiation therapy and immunotherapy, according to the American Cancer Society.
In chronic myelogenous leukemia, or CML, scientists have identified a genetic mutation involved in the disease. A drug has been developed that specifically targets the mutation and by taking the medication daily, the cancer can be kept under control, Vaiselbuh said.
Acute lymphocytic leukemia, or ALL, is the most common leukemia in children and has the highest survival rates — more than 90 percent for children under 5 years old and 66.4 percent for patients of all ages, according to the National Cancer Institute.
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