Claim: Smoking is correlated with the occurrence of leukemia.

Leukemia , also spelled leukaemia , is a group of cancers that usually begin in the bone marrow and result in high numbers of abnormal white blood cells . These white blood cells are not fully developed and are called blasts or leukemia cells . 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 blood tests or bone marrow biopsy .   The exact cause of leukemia is unknown . Different kinds of leukemia are believed to have different causes . Both inherited and environmental -LRB- non-inherited -RRB- factors are believed to be involved . Risk factors include smoking , ionizing radiation , some chemicals -LRB- such as benzene -RRB- , prior chemotherapy , and Down syndrome . People with a family history of leukemia are also at higher risk . There are four main types of leukemia -- acute lymphoblastic leukemia -LRB- ALL -RRB- , acute myeloid leukemia -LRB- AML -RRB- , chronic lymphocytic leukemia -LRB- CLL -RRB- and chronic myeloid leukemia -LRB- CML -RRB- -- as well as a number of less common types . Leukemias and lymphomas both belong to a broader group of tumors that affect the blood , bone marrow , and lymphoid system , known as tumors of the hematopoietic and lymphoid tissues .   Treatment may involve some combination of chemotherapy , radiation therapy , targeted therapy , and bone marrow transplant , in addition to supportive care and palliative care as needed . Certain types of leukemia may be managed with watchful waiting . The success of treatment depends on the type of leukemia and the age of the person . Outcomes have improved in the developed world . The average five-year survival rate is 57 % in the United States . 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 .   In 2015 , leukemia was present in 2.3 million people and caused 353,500 deaths . In 2012 it newly developed in 352,000 people . It is the most common type of cancer in children , with three quarters of leukemia cases in children being the acute lymphoblastic type . However , about 90 % of all leukemias are diagnosed in adults , with AML and CLL being most common in adults . It occurs more commonly in the developed world .