ALL is a relatively rare disease in adults, representing approximately 20% of adult acute leukemias. The estimated number of new cases of ALL in the year 2003 in the United States was 3600. The age-adjusted incidence is 1.6 per 100,000 in adults.2 There is a bimodal distribution to the incidence of the disease, with an initial peak in early childhood and a second smaller peak in patients older than 50 years.3 Secondary acute leukemias can occur following chemotherapy or radiation treatment for other malignancies. Although most of these leukemias are myeloid, an increasing number of ALL cases are being reported following exposure to chemotherapy with topoisomerase II inhibitors. These therapy-related ALL cases have been associated with chromosomal rearrangements involving the MLL gene and typically occur within 2 years of initial exposure to the chemo therapeutic agent(s).4 A longer time to development of leukemia has been observed following exposure to alkylating agents and the development of therapy-related leukemias.

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