Molecular Diagnosis of the Philadelphia Chromosome in Acute Lymphoblastic Leukemia

Factors involved in leukaemogenesis and haemopoiesis

This review describes the chromosomal abnormalities in T-cell acute lymphoblastic leukaemia (ALL) which result in the over-expression of the gene SCL, which encodes a helix-loop-helix transcription factor. Also described are how gene targeting studies have revealed a key role for SCL in normal haemopoiesis. Next, the BCR-ABL fusion protein, seen in chronic myeloid leukaemia (CML) and in some patients with ALL, is discussed. Finally, the involvement of members of the core-binding factor (CBF) gene family in leukaemogenesis are described. Members of this gene family are involved in the generation of fusion proteins as a result of t(8;21) and inv(16), the most common translocations associated with acute myeloid leukaemia (AML). They provide a useful model of the way in which aberrant transcriptional function, brought about through genetic alterations, can modify haemopoietic development.

Ph positive acute lymphoblastic leukemia in adults: molecular and clinical studies

Fifty-six patients with ALL were investigated for bcr involvement by PCR. Breakpoints were found in 15 patients (26.8%). There were no differences in clinical and hematologic features or the percentages of complete response (CR) between the Ph+ and Ph- cases. The duration of CR was 6 and 8 months, respectively. In 7/9 Ph1 relapsed ALL we observed increased expression of myeloid markers and 2/9 showed a switch of cytotype (Ly-->My). In none of the 13 Ph- relapsed ALL patients did we observe these findings. 7/15 of Ph+ cases expressed P190 and mRNA ela2 and 8/15 patients showed P210, with mRNA b3a2 in 5 and b2a2 in 3, respectively. The percentage of CR was 57% in the P190+ and 87% in the P210+ group. Investigation of more Ph1+ ALL cases treated with a uniform protocol should be performed in the future in order to determine whether any such biological and clinical differences exist.

Repeated PCR in CML during IFN-alpha therapy

Repeated PCR analysis was performed on bone marrow and/or peripheral blood samples from 4 CML patients in complete cytogenetic remission during treatment with IFN-alpha. Two patients became PCR-negative. One was negative for the analyses carried out from the 9th to the 30th months, but reverted to PCR positivity 10 months after IFN was reduced from 1.5 x 10(6) IU/day to 1 x 10(6) IU and given on alternate days. Although the dose was again raised to 3 x 10(6) IU/day, 8 months later her peripheral blood cells were still PCR-positive, but remained persistently Ph'-negative. Another patient became PCR-negative at the 42nd month and remained so at the last analysis performed 3 months later. Two patients were persistently PCR-positive. Cytogenetic relapse was documented in both, in one while still on full therapy. Ph'-positive metaphases reappeared in the other patient 7 months after discontinuing IFN-alpha therapy.

High incidence of meningeal leukemia in lymphoid blast crisis of chronic myelogenous leukemia

Fifteen patients with lymphoid blast crisis of chronic myelogenous leukemia (LyBC-CML) and five patients with acute lymphoblastic leukemia converting to Philadelphia-positive (Ph+) chronic myeloid leukemia (ALL Ph + CML) were followed. Seven of 15 (46.7%) LyBC-CML patients developed meningeal leukemia within a median period of 6 months (range 2-11 months), while there was no medullary relapse. Five of these responded well to triple intrathecal therapy. In the ALL Ph + CML patients, in spite of central nervous system (CNS) prophylaxis with IT MTX and 18 Gy cranial radiation, two of five patients (40%) experienced meningeal leukemia, one isolated and the other with medullary relapse. The data confirm that LyBC-CML patients experience a high incidence of meningeal leukemia. The role of CNS prophylaxis is not very clear, but its use may delay development and reduce morbidity due to CNS disease.

The role of molecular techniques in the clinical management of leukemia. Lessons from the Philadelphia chromosome

The Philadelphia chromosome (Ph1) was the first genetic change to be associated consistently with leukemia, and it is one of the best understood on the molecular level. Because of this, it is an excellent model to investigate the application of molecular techniques to the clinical setting. These techniques are reviewed as are their clinical use in chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL), and transplantation. The Ph1 is caused by the fusion of two genes on chromosomes 9 and 22, resulting in the BCR-ABL fusion gene. This new gene is believed to be the cause of these Ph1-positive leukemias. The ability to detect the BCR-ABL fusion gene evolved from cytogenetic detection to Southern blot analysis, and now includes sophisticated techniques such as polymerase chain reaction (PCR) methods and pulsed-field gels. Diagnosis of the BCR-ABL fusion gene by Southern blot detection of bcr genetic rearrangements is the prototype of molecular cancer diagnosis. The sensitivity and clinical uses of this test are reviewed, especially its application to monitoring the response to treatment. PCR methods enable the researcher to detect 1 CML cell in a population of 10(5) cells. Clinical experience with PCR, especially in transplantation medicine, is providing a better understanding of the meaning of the terms "remission" and "cure." Newer techniques using fluorescent in situ hybridization have considerable potential for BCR-ABL detection, but no clinical experience has been gained with these techniques currently. The diagnosis of the BCR-ABL fusion gene in ALL has important clinical implications because it is the most common molecular genetic change in adult ALL and is associated with short remissions and poor outcome in all age groups. Diagnosis of the BCR-ABL fusion in ALL is difficult because the molecular findings are more heterogeneous than they are in CML. The methods available and their accuracy and sensitivity are compared. A review of their clinical impact is included.

Cytogenetic abnormalities in childhood acute lymphoblastic leukemia correlates with clinical features and treatment outcome

Virtually all cases of childhood acute lymphoblastic leukemia have chromosomal abnormalities. Non-random chromosomal abnormalities have been correlated with leukemic cell lineage, the degree of cell differentiation and certain clinical and biologic features. Cytogenetic findings have prognostic significance, but the adverse influence of many rearrangements, including most chromosomal translocations, may be offset by the greater cytoreductive effects of intensified therapy. Cytogenetic abnormalities have also provided focus for molecular studies of leukemogenesis. Such studies have recently identified key genes and their protein products which play important roles in malignant transformation and proliferation.

Ewing's sarcoma t(11;22) in a case of acute nonlymphocytic leukemia

Chromosome analysis of bone marrow cells from a patient with acute nonlymphocytic leukemia M2 revealed the translocation t(11;22)(q24;q12) usually associated with Ewing's sarcoma. Molecular investigations ruled out the possibility that this was a variant Philadelphia translocation with breakpoints in the major breakpoint cluster region. Although cytogenetic analysis was not available at diagnosis, this abnormality was found both pre- and postallogeneic bone marrow transplant.

Studies of BCR rearrangements in Philadelphia-positive acute leukemia

Five patients with Philadelphia-positive acute leukemia were cytogenetically and molecularly investigated in order to determine the localization of the breakpoints on chromosome 22. Rearrangements of the bcr segment were detected in one case with acute mixed leukemia in a child. Rearrangements in the BCR gene first intron, the so-called bcr2 and bcr3 regions, were detected in two other cases, one with an acute lymphoblastic leukemia (ALL) and one with mixed acute leukemia. No molecular rearrangement could be detected in the last two cases, an ALL and a T-cell acute lymphoblastic leukemia with a t(2;22) translocation.