Childhood Acute Myeloid Leukemia Treatment (Professional) (cont.)
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Therapy-Related AML/Myelodysplastic Syndromes
The development of acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS) following treatment with ionizing radiation or chemotherapy, particularly alkylating agents and topoisomerase inhibitors, is termed therapy-related (t-AML or t-MDS, respectively). In addition to genotoxic exposures, genetic predisposition susceptibilities (such as polymorphisms in drug detoxification and DNA repair pathway components) may contribute to the occurrence of secondary AML/MDS.[1,2,3,4] The risk of t-AML/t-MDS is regimen-dependent and is related to the cumulative doses of chemotherapy agents received, as well as the dose and field of radiation administered. Regimens previously used that employed high cumulative doses of either epipodophyllotoxins (e.g., etoposide or teniposide) or alkylating agents (e.g., mechlorethamine, melphalan, busulfan, and cyclophosphamide) induced excessively high rates of t-AML/t-MDS that exceeded 10% in some cases.[5,6] However, most current chemotherapy regimens that are used to treat childhood cancers have a cumulative incidence of t-AML/t-MDS not greater than 1% to 2%. t-AML/t-MDS resulting from epipodophyllotoxins and other topoisomerase II inhibitors (e.g., anthracyclines) usually occur within 2 years of exposure and are commonly associated with chromosome 11q23 abnormalities, although other subtypes of AML (e.g., acute promyelocytic leukemia) have been reported.[8,9] t-AML following exposure to alkylating agents or ionizing radiation often occurs 5 to 7 years later and is commonly associated with monosomies or deletions of chromosomes 5 and 7.[1,7]
The goal of treatment is to achieve an initial complete remission (CR) using AML-directed regimens and then, usually, proceed directly to hematopoietic stem cell transplantation (HSCT) with the best available donor. However, treatment is challenging due to the following:
Accordingly, CR rates and overall survival (OS) rates are usually lower for patients with t-AML compared with patients with de novo AML.[10,11,12] Patients with t-MDS-refractory anemia usually have not needed induction chemotherapy prior to transplant; the role of induction therapy with refractory anemia with excess blasts-1 prior to transplant is controversial.
Only a few reports describe the outcome of children undergoing HSCT for t-AML. One study described outcomes of 27 children with t-AML who received related and unrelated donor HSCT. Three-year OS rates were 18.5% ± 7.5% and event-free survival rates were 18.7% ± 7.5%. Poor survival was mainly due to very high transplant-related mortality (59.6% ± 8.4%). Another study reported a second retrospective single-center experience of 14 patients transplanted for t-AML/t-MDS between 1975 and 2007. Survival was 29%, but in this review only 63% of patients diagnosed with t-AML/t-MDS underwent HSCT. A multicenter study (CCG-2891) looked at outcomes of 24 children with t-AML/t-MDS compared with other children enrolled on the study with de novo AML (n = 898) or MDS (n = 62). Children with t-AML/t-MDS were older and low-risk cytogenetics rarely occurred. Although rates of achieving CR and OS at 3 years were worse in the t-AML/t-MDS group (CR, 50% vs. 72%, P = .016; OS, 26% vs. 47%, P = .007), survival was similar (OS, 45% vs. 53%, P = .87) if patients achieved a CR. The importance of remission to survival in these patients is further illustrated by another single-center report of 21 children undergoing HSCT for t-AML/t-MDS between 1994 and 2009. Of the 21 children, 12 had t-AML (11 in CR at the time of transplant), seven had refractory anemia (for whom induction was not done), and two had refractory anemia with excess blasts. Survival of the entire cohort was 61%; those in remission or with refractory anemia had a disease-free survival of 66%, and for those with more than 5% blasts at the time of HSCT, survival was 0% (P = .015). Because t-AML is rare in children, it is not known whether the significant decrease in transplant-related mortality after unrelated donor HSCT noted over the past several years will translate to improved survival in this population. Patients should be carefully assessed for pre-HSCT morbidities caused by earlier therapies and approaches should be adapted to give adequate intensity while minimizing transplant-related mortality.
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