Detection of minimal residual disease in acute leukemia patients

Diagnostic techniques, routinely used in clinical practice for monitoring acute leukemia patients, are able to detect only 1-5% of malignant cells. At present, two main techniques are being introduced for detection of minimal residual disease (MRD) in leukemia, namely immunological marker analysis and the polymerase chain reaction (PCR) technique with general sensitivity of 10(-4)-10(-5). Immunological marker analysis allows detection of unusual and aberrant immunophenotypes, and is usually performed by flow cytometry. PCR analysis allows detection of leukemia-specific DNA sequences, such as fusion regions of chromosome asberrations and junctional regions of rearranged immunoglogulin (Ig) genes and T-cell receptor (TcR) genes. The applicability of the immunophenotyping and PCR-mediated MRD techniques is dependent on the type of leukemia. In virtually all acute lymphoblastic leukemias, PCR analysis of 18 and TcR genes can be used, and immunophenotypic MRD detection is also possible in 70-80% of cases. In AML, immunophenotypic MRD detection can be applied in approximately 80% of cases and PCR analysis of chromosome aberrations in 25-40%. Each MRD technique has its advantages and limitations, which have to be weighed carefully to make an appropriate choice. Furthermore, standardization of the MRD techniques is needed before they are used for stratification or adaptation of treatment protocols. Finally, the clinical impact of MRD detection for the various subtypes of acute leukemias has to be established.