Hematopoietic malignancies account for 6% to 8% of new cancers diagnosed annually. In the year 2009, an estimated 44,790 new cases of leukemia were diagnosed, and 21,870 deaths were attributable to leukemias of all types. The total age-adjusted incidence of leukemia, including both acute and chronic forms, is 9.6 per 100,000 population; the incidence of acute lymphoblastic leukemia (ALL) is 1.5 per 100,000 and of acute myelogenous leukemia (AML) is 2.7 per 100,000 population.

Epidemiology

Gender The incidence of both ALL and AML is slightly higher in males than in females.

Age The age-specific incidence of AML is similar to that of other solid tumors in adults, with an exponential rise after age 40. With regard to ALL, 60% of cases are seen in children, with a peak incidence in the first 5 years of life and a subsequent drop in incidence until age 60, when a second peak emerges.

Race and ethnicity The incidence of acute leukemia is slightly higher in populations of European descent. Also, a report from the University of Southern California indicates that acute promyelocytic leukemia (APL) is more common in Hispanic populations than in other ethnic groups.

Etiology and risk factors

There is wide diversity in the behavior of the various subsets of acute leukemias. Thus, it is unlikely that there is one common etiology for these aberrant cellular proliferations. There are, however, some accepted risk factors for leukemogenesis.

Chemical exposure The increased incidence of AML and myelodysplasia (preleukemia) has been reported in persons with prolonged exposure to benzene and petroleum products. The interval between exposure and the onset of leukemia is long (10 to 30 years). Chromosomal damage is common.

Pesticide exposure also has been linked to some forms of AML. The incidence of AML is beginning to rise in developing countries, as industrialization and pollution increase.

Other environmental exposures Exposure to hair dyes, smoking, and nonionic radiation may also increase the risk of leukemia.

Prior chemotherapy or irradiation Use of alkylating agents, such as cyclophosphamide and melphalan (Alkeran), in the treatment of lymphomas, myelomas, and breast and ovarian cancers has been associated with the development of AML, usually within 3 to 5 years of exposure and often preceded by a myelodysplastic phase. Cytogenetic abnormalities, particularly monosomy 5, 7, 11, and 17, are common. Concurrent radiation exposure slightly increases the risk of leukemogenesis posed by alkylating agents.

Topoisomerase II inhibitors (etoposide, teniposide [Vumon], doxorubicin and its derivatives, and mitoxantrone, used to treat ALL, myeloma, testicular cancer, and sarcomas, as well as taxanes used to treat breast cancer, have also been implicated in leukemogenesis. These agents, in contrast to alkylators, are associated with a short latency period without antecedent myelodysplasia and with cytogenetic abnormalities involving chromosome 11q23 or 21q22 in the malignant clone.

Genetic disorders An increased incidence of AML is seen in patients with Down syndrome, Bloom syndrome, or Fanconi's anemia, as well as in individuals with ataxia-telangiectasia or Wiskott-Aldrich syndrome. In identical twins younger than age 10, if one child develops leukemia (usually ALL), there is a 20% chance that the other twin will develop leukemia within a year; subsequently, the risk falls off rapidly and joins that of nonidentical siblings, which is three to five times that of the general population.