Introduction

As a result of combination chemotherapy administered from several months to 2–3 years, depending upon the type of malignancy and risk stratification, the cure rate in children with acute lymphoblastic leukemia (ALL) who are younger than 15 years of age has risen from less than 10% in the pre-chemotherapy era to 88% presently [1]. Moreover, the cure rate for acute myeloid leukemia (AML), although not as successful, has also markedly improved. This success came mostly as a result of randomized clinical trials conducted by the Children's Oncology Group (COG), the St. Jude Children's Research Hospital, the Medical Research Council in the United Kingdom, and the German Berlin–Frankfurt–Münster clinical trials group. However, while the chemotherapy is necessary for a cure, most of the chemotherapeutic agents have serious myelosuppressive effects resulting in short- and long-term abnormalities in the peripheral blood and bone marrow. Knowledge of these changes is essential for the proper evaluation of such specimens in children undergoing chemotherapy.

Factors affecting treatment response

The treatment response and leukemia clearance differ depending on multiple factors associated with the host response to chemotherapy. Recent studies have shown that these differences in response to drugs are due to individual genomic variations such as single nucleotide polymorphisms (SNPs), insertion, inversions, copy-number variations, epigenetic variants, or loss of heterozygosity that are able to influence the absorption, distribution, metabolism, and excretion of chemotherapeutic agents [2] (Table 19.1 [3]).