The incidence of secondary leukemias

The term secondary leukemia is usually employed to indicate both forms of acute myeloid leukemia (AML) evolving from previous myelodysplasia and forms of acute leukemia developing after exposure to environmental or therapeutic toxins or radiation (therapy related). Secondary leukemias account for 10-30% of all AML. The majority of secondary leukemias resulting from the use of cytotoxic drugs can be divided into two well defined groups depending on whether the patient has received 1) alkylating agents or 2) drugs binding to the enzyme DNA-topoisomerase II. Alkylating agents related leukemias are very similar to post MDS leukemias being characterized frequently by a preleukemic phase, tri-lineage dysplasia, frequent cytogenetic abnormalities involving chromosomes 5 and 7 and a poor prognosis. Secondary leukemias related to therapy with topoisomerase II inhibitors are not preceded by a preleukemic phase and show frequently balanced translocations involving chromosome 11q23. Among therapy-related leukemias, AML is generally a second neoplasm, thus a predisposition to malignancy, independently from previous chemotherapy, cannot be excluded. This review article examines the incidence of all secondary AMLs and the risk of therapy-related leukemia in relation to the different primary malignancies and treatments.

The authors have been working in this field, both experimentally and at clinical level, contributing original papers for many years. In addition, the material examined in this review includes articles published in journals covered by MedLine, reviews in journals with high impact factor and recent reports presented at the Secondary Leukemia. An Update Symposium held in Rome in November 1998.

The incidence of secondary leukemias is increasing because of aging of the population (MDS is more frequent in elderly people) and widespread and successful use of chemoradiotherapy in cancer patients. In the GIMEMA archive of adult acute leukemia (2,964 AML pts from June 1992 to June 1996) an antecedent hematologic disorder (AHD) and/or MDS was found in 8% of all patients (10% of 2,118 patients aged more than 45 years and in 4% of 848 patients aged less than 45). In this series of patients, 6% of all myeloid leukemias were therapy-related leukemia. Therapy-related leukemias are a major problem in patients treated for Hodgkin's disease, non-Hodgkin's lymphoma, myeloma, polycythemia, breast cancer, ovarian carcinoma, or testicular carcinoma. In the GIMEMA archive more than 50% of patients with secondary AML have breast cancer, NHL, and HD. Alkylating agents, nitrosureas and procarbazine appear to have the highest leukemogenic potential. Furthermore aggressive chemotherapy and radiotherapy followed or not by hematopoietic stem cell infusion will produce a more and more prolonged survival but also a greater incidence of secondary AML. Assessment of the risk of secondary leukemia should become part of any therapeutic plan for cancer patients. Avoidance of drugs with more leukemogenic potential will produce a marked reduction of secondary AML.