Philadelphia chromosome-positive acute lymphoblastic leukemia.

The Philadelphia (Ph1) chromosome, ubiquitous in chronic myelogenous leukemia, also is commonly seen in acute lymphoblastic leukemia, particularly in adults. Whereas the presence of the Ph1 chromosome is associated with high white blood cell count and older age, the Ph1 chromosome is known to be an independent poor prognostic factor. Most Ph1+ patients are able to achieve remissions with intensive, systemic chemotherapy, but treatment is complicated by early relapse. Because of the uniformly poor prognosis and response to therapy in childhood and adult Ph1+ acute lymphoblastic leukemia, aggressive and investigational therapies should be considered early in the course of this disease.

Clinical significance of the BCR-ABL fusion gene in adult acute lymphoblastic leukemia: a Cancer and Leukemia Group B Study (8762).

The Philadelphia (Ph1) chromosome, or its molecular counterpart, the BCR-ABL fusion gene, is a rare but important prognostic indicator in childhood acute lymphoblastic leukemia (ALL), but its impact on adult ALL has not been well ascertained. A prospective study of the BCR-ABL fusion gene was begun on patients entered on clinical trials conducted by the Cancer and Leukemia Group B (CALGB). All patients received intensive, multiagent chemotherapy that included daunorubicin. Over 2 years, 56 patients were studied for molecular evidence of a BCR-ABL gene using Southern blot and pulsed-field gel hybridization analysis. Results were compared with cytogenetic detection of a Ph1 chromosome, and clinical features were compared for the BCR-ABL-positive and -negative groups. Molecular methods detected the BCR-ABL gene in 30% of cases compared with cytogenetic detection of the Ph1 chromosome in only 23%. The majority of cases (76%) showed the p190 gene subtype similar to pediatric ALL; the BCR-ABL-positive cases displayed a more homogeneous immunophenotype than the BCR-ABL-negative cases and were predominantly CALLA positive (86%) and B-cell surface antigen positive (82%). The rate of achieving complete remission was similar in the BCR-ABL-positive and -negative groups (71% and 77%, respectively, P = .72). There were more early relapses in the BCR-ABL-positive group, resulting in a shorter remission duration that was especially marked in the CALLA-positive and B-cell antigen-positive populations. These preliminary data suggest that the impact of the BCR-ABL gene on clinical outcome in ALL may be on maintenance of complete remission (CR) rather than achievement of CR when aggressive, multiagent chemotherapy is used. This study identifies the BCR-ABL gene as an important factor in adult ALL and demonstrates the utility of molecular methods for its accurate diagnosis.

The use of the polymerase chain reaction in clinical oncology.

The polymerase chain reaction (PCR) is an extraordinary tool for studying cancer. It is both more sensitive and more rapid than any other detection method, and can be performed without special expertise. It is ideal for the detection of minimal residual disease, particularly in lymphoid malignancies, but also for any cancer with a genetic abnormality that is defined at the molecular level. Other uses, such as diagnosis of cancer based on detection of translocations or point mutations, have an intriguing potential, but remain investigational. At this point, few clinicians would be willing to base a diagnosis, let alone a treatment plan, on a diagnosis based on PCR findings without confirming histology.

Interphase cytogenetic analysis detects minimal residual disease in a case of acute lymphoblastic leukemia and resolves the question of origin of relapse after allogeneic bone marrow transplantation.

We used in situ hybridization with a probe for the X chromosome to study interphase cells of bone marrow and peripheral blood specimens from a male patient with acute lymphoblastic leukemia characterized by hyperdiploidy, including trisomy X. In a posttreatment bone marrow specimen, which was interpreted as a regenerating bone marrow morphologically and which demonstrated a normal karyotype cytogenetically, trisomy X was found in 16 of 1,000 interphase cells. This finding indicated the presence of leukemic cells that were undetected by conventional morphologic and cytogenetic techniques (ie, minimal residual disease). Cytogenetic studies of a relapse specimen obtained after a sex-mismatched bone marrow transplant showed only a normal female karyotype in each of 40 metaphase cells, suggesting that the relapse occurred in donor cells. However, interphase analysis demonstrated trisomy X in more than 80% of interphase cells and indicated that the relapse was of the original clone and was not a transformation of donor cells. This case illustrates that interphase analysis can be useful as an adjunct to conventional cytogenetic analysis in the detection of minimal residual disease and in the analysis of interphase cells that are not accessible to routine cytogenetic methods. It also illustrates that previously reported instances of relapse of leukemia in donor cells could have been incorrect if supported by cytogenetic data alone.

Molecular methods to detect the Philadelphia chromosome.

The Ph1 chromosome has two molecular subtypes: a bcr-positive seen in CML and some cases of ALL, and the bcr-negative subtype mainly seen in ALL. In CML, because of the restriction of chromosome 22 breakpoints to the bcr, Southern analysis to detect bcr rearrangements also can be used to detect the Ph1 chromosome. In contrast, the translocation breakpoints on the Ph1 chromosome are scattered in ALL, so that other methods such as PFGE and PCR are necessary to detect the Ph1 chromosome. In both CML and ALL, use of these methods to detect molecular abnormalities may be superior to cytogenetics in detecting chromosomal abnormalities. Southern analysis also can be used in CML to map breakpoint locations within the bcr. This may offer prognostic information as to the length of chronic phase, but there is conflicting information as to the validity of this approach. The modified PCR (using cDNA from mRNA) can be used to detect the Ph1 chromosome and to define which of the molecular subtypes are present. The exquisite sensitivity of this method, which is capable of detecting as little as a single abnormal molecule of RNA or DNA, makes it suited for the detection of minimal residual disease in both CML and ALL. This is particularly useful after intensive therapies, such as bone marrow transplantation. Whether these low levels of fusion gene expression are of prognostic significance is still unclear.

Detection of the Philadelphia chromosome in acute lymphoblastic leukemia by pulsed-field gel electrophoresis.

The Philadelphia (Ph1) chromosome is an acquired abnormality in the malignant cells of 10% to 25% of patients with acute lymphoblastic leukemia (ALL). Unlike chronic myelogenous leukemia (CML), where the molecular detection of the Ph1 chromosome is relatively straightforward using conventional Southern hybridization analysis, the detection of the Ph1 chromosome in ALL is complicated by the existence of several molecular subtypes, and the fact that translocation breakpoints are dispersed over a large genomic area. To circumvent these difficulties, we investigated pulsed-field gel electrophoresis (PFGE) to determine if this method could be used directly on clinical samples to detect the Ph1 chromosome in ALL. We report that, in a study of seven patients with Ph1-positive ALL, we could easily detect the Ph1 using only a single PFGE analysis, regardless of the Ph1 subtype, and we could confirm that the translocations occur either within or very near the BCR gene in all seven. We conclude that PFGE is a useful technique for the detection of the Ph1 in ALL, which ultimately may find wide applicability in the detection of other chromosomal abnormalities in other malignancies.

Unexpected heterogeneity of BCR-ABL fusion mRNA detected by polymerase chain reaction in Philadelphia chromosome-positive acute lymphoblastic leukemia.

The Philadelphia (Ph1) chromosome results in a fusion of portions of the BCR gene from chromosome 22 and the ABL gene from chromosome 9, producing a chimeric BCR-ABL mRNA and protein. In lymphoblastic leukemias, there are two molecular subtypes of the Ph1 chromosome, one with a rearrangement of the breakpoint cluster region (bcr) of the BCR gene, producing the same 8.5-kilobase BCR-ABL fusion mRNA seen in chronic myelogenous leukemia (CML), and the other, without a bcr rearrangement, producing a 7.0-kilobase BCR-ABL fusion mRNA that is seen only in acute lymphoblastic leukemia (ALL). We studied the molecular subtype of the Ph1 chromosome in 11 cases of Ph1-positive ALL, including 2 with a previous diagnosis of CML, using a sensitive method to analyze the mRNA species based on the polymerase chain reaction (PCR). We observed unexpected heterogeneity in BCR-ABL mRNA in this population; in particular, 1 of 6 bcr-rearranged cases and 1 of 5 bcr-unrearranged cases contained none of the known fusion mRNA species, while 1 of the bcr-rearranged cases contained both. This latter case is particularly interesting because it suggests that the acquisition of an additional BCR-ABL fusion species may be a mechanism of disease progression. We conclude that the PCR gives additional information about the Ph1 chromosome gene products that cannot be obtained by genomic analysis, but that it cannot be used as the sole means of detection of this chromosomal abnormality in ALL because of the high incidence of false negative results.

Molecular Diagnosis of the Philadelphia Chromosome in Acute Lymphoblastic Leukemia.

The Philadelphia (Ph(1)) chromosome was the first specific chromosomal abnormality to be consistently associated with a particular neoplasm, in this case chronic myelogenous leukemia (CML,)(1). Formed by a reciprocal translocation between chromosomes 9 and 22(2), the 22q-, or Ph(1) chromosome is found in the malignant cells of more than 90% of patients with CML(3). The presence of the molecular equivalent of a Ph(1) chromosome is such a consistent finding in CML that it IS now the basis of a diagnostic test in routine clinical use.