Cytogenetic and molecular characterization of a masked Philadelphia chromosome in chronic myelocytic leukemia

A case of typical chronic myeloid leukemia with an apparently Philadelphia-negative karyotype is described. Molecular studies confirmed the cytogenetic interpretation of a standard Ph rearrangement, with secondary involvement of 22q- in a translocation with chromosome #5, leading to its masking. The chromosomal regions engaged in the standard t(9;22) were not modified and the molecular rearrangements of Ph were also conserved. The hematologic and clinical features were apparently not influenced by the events leading to the masking of Ph. Further similar observations with both cytogenetic and molecular characterization are needed to better identify the possible clinical consequences of these complex changes.     

A case of chronic myeloid leukemia with a "masked" Philadelphia chromosome

A case is described of a 67-year-old man with chronic myeloid leukemia and a "masked" Philadelphia chromosome due to a translocation between chromosomes #4 and #22. The significance of this case in relation to the possible pathogenesis of chronic myeloid leukemia is discussed.     

Cytogenetic and molecular studies in patients with chronic myeloid leukemia and variant Philadelphia translocations

Out of 105 Philadelphia (Ph) positive chronic myeloid leukemia patients analyzed, six (5.7%) carried a variant Ph translocation, namely t(6;9;9;10;22)(q24;p13;q34;p15;q11); t(9;13;22)(q34;q21;q11);der(2)(2pter----2q31::9q21---- 9q34::22q11----22qter) and der(9)t(2;9) (9pter----9q21::2q31----2qter);t(7;9;22)(q11;q34 ;q11), 14q + ;t(7;9;22)(q35;q34;q11), and t(9;11;22) (q34;q13;q11), respectively. Five of these patients were analyzed with Southern blotting. Three of them showed an atypical molecular pattern; namely, the patient with t(9;13;22) showed no rearrangement in the breakpoint cluster region (bcr), the patient with t(7;9;22)(q35;q34;q11) showed a 3' deletion, and the patient with t(7;9;22), 14q + showed a bcr rearrangement 3' to the exon 4 of the M-BCR. Chromosome in situ hybridization studies demonstrated that in patient one, a two-step translocation occurred: the first step moved the 3' bcr from chromosome 22 to chromosome 9, and the second moved the terminal part of 22q, carrying the c-sis protooncogene, to 10p. Variant Ph translocations appear to be associated with atypical molecular breakpoints.     

Chromosomal characteristics of chronic and blastic phases of Ph-positive chronic myeloid leukemia

To evaluate the appearance of chromosome changes, in addition to the Philadelphia (Ph) chromosome, as predictive and diagnostic parameters of transformation in chronic myeloid leukemia (CML), such changes were analyzed in the chronic phase (CP) and compared with those of the blastic phase (BP) of CML. The common chromosome changes observed in the CP were loss of a Y (-Y), trisomy 8 (+8), an isochromosome for the long arm of chromosome #17 [i(17q)], a double Ph (+Ph), reciprocal translocations, and partial deletions. In most patients with chromosome changes in addition to the Ph, the percentage of abnormal clones increased steadily during the CP and was accompanied by other chromosome changes shortly before or at the onset of the BP, except for cases with -Y or i(17q) clones. In general, most chromosome changes observed shortly before or at the BP were complex. These facts suggest that complex chromosome changes could be utilized as predictive and diagnostic parameters of blastic transformation in CML.     

Breakpoint cluster region rearrangements in chronic myelogenous leukemia with a masked Philadelphia chromosome

Cytogenetic and molecular analyses were performed in a case of chronic myelogenous leukemia. The cytogenetic study revealed that the leukemic cells of this patient contained a three-way translocation involving chromosomes #5, #9, and #22, resulting in a masked Philadelphia chromosome; the karyotype of the leukemic cells was 46,XY,t(5;22;9)(q31;q11;q34). Southern blot analysis of leukemic cell DNA was performed using a 1.1 kb HindIII-EcoRI breakpoint cluster region (bcr) probe. The results showed that BglII digested DNA showed two abnormal bcr fragments (i.e., 5.2 kb and 2.7 kb) in contrast to the results with DNA from two patients with a standard Ph chromosome [t(9;22)(q34;q11)] who showed one normal 5.0-kb bcr fragment in addition to altered fragments of about 4.3 kb or 4.0 kb. Bam HI digests of DNA from the leukemic cells of the patient with the masked Ph chromosome showed two bands (3.3 kb and 6.5 kb), whereas, DNA from the two patients with standard Ph translocations showed only a 3.3-kb bcr fragment. The results indicate that the molecular events in a masked Ph affect the bcr locus in a manner similar to that seen in standard Ph chromosomes.     

Cytogenetic follow-up of patients with nonlymphocytic leukemia I. Philadelphia chromosome-positive chronic myeloid leukemia

Chromosomes of blood and bone marrow cells were studied in 53 patients with Philadelphia chromosome (Ph¹)-positive chronic myeloid leukemia (CML). Fifty patients presented with t(9;22) and three with variant translocations: t(17p+;22q?); t(17q+;22q?), and t(1;9;22). Serial studies were carried out in 27 patients during both the chronic and the blastic phase of the disease. Five patients in the chronic phase developed cytogenetic changes in addition to the Ph¹. In two of these cases the changes preceded a transformation into acute leukemia, but in three cases no acceleration of the disease has occurred 1 to 4 years after the emergence of the subclones. Blastic transformation occurred in 15 instances; 11 of these patients acquired additional nonrandom chromosomal changes: trisomy 8 (9 times), i(17q) (4 times), trisomy 17 (2 times), trisomy 19 (7 times), and duplication of the 22q? (6 times). Clonal evolution was found in eight cases, either at the onset of blastic transformation or later in follow-up cultures. The differences between karyotypic evolution during the chronic and blastic phases of CML are discussed, together with their prognostic significance.     

A cytogenetic and molecular analysis of five variant Philadelphia translocations in chronic myeloid leukemia

Three patients had complex translocations involving 9q34, 22q11, and a third chromosome (Xq11, 7q11.2, or 15q11.2). Two patients had apparently simple variant Philadelphia (Ph) translocations, t(19;22) and t(11;22), with no obvious involvement of chromosome 9, and the Ph was masked in the t(11;22). In situ hybridization studies showed transposition of the abl gene from chromosome 9q34 to the breakpoint cluster region (bcr) of chromosome 22 in all five patients; this was confirmed by rearrangements of the bcr gene in leukemic DNA. In situ hybridization also showed that the bcr-3' and c-sis probes consistently translocated to recipient chromosomes X, 1, 7, 11, and 15, whereas IgC lambda remained on chromosome 22q. These results confirm that association of abl and bcr is a consistent feature of chronic myeloid leukemia irrespective of the cytogenetic presentation and support the conclusion of Hagemeijer that all simple variant Ph translocations are, in fact, complex and involve at least three chromosomes.     

A t(3;5) in blastic phase of a Philadelphia chromosome-negative chronic myeloid leukemia

Serial cytogenetic analyses from the bone marrow of a patient with blastic phase of a Philadelphia chromosome-negative chronic myeloid leukemia revealed a t(3;5)(p21;q31). The literature on translocations involving chromosome 3 and the long arm of chromosome 5 is reviewed. The importance of breakpoints in band 5q31 is discussed.     

Translocation of c-abl to "masked" Ph in chronic myeloid leukemia

In two patients with chronic myeloid leukemia (CML), the nature of the chromosomal rearrangement giving rise to "masked" Ph has been studied by in situ hybridization of human c-abl sequences. The c-abl probes hybridized to the 22q11 region of the "masked" Ph, demonstrating that translocation of sequences from 9q34 to the Ph did occur exactly as in standard Ph or in other types of variants previously studied. These results provide additional evidence for the occurrence of a constant molecular rearrangement in Ph-positive CML.     

Cytogenetic follow-up in chronic myeloid leukemia

Twenty-six patients with Philadelphia chromosome (Ph¹)-positive chronic myeloid leukaemia have been followed up cytogenetically. Twelve patients were found to have chromosome abnormalities in addition to the Ph¹, either in the chronic phase or during progression of disease. The most common abnormality observed was an additional chromosome No. 19 although trisomy 8, a second Ph¹ and isochromosome 17 were also observed.     

BCR/ABL fusion located on chromosome 9 in chronic myeloid leukemia with a masked Ph chromosome

A reciprocal translocation, t(10; 22) (q22; q11), resulting in a masked Ph chromosome was identified in a patient diagnosed with chronic myeloid leukemia (CML). Both homologs of chromosome 9 were of the normal pattern. Two signals for the ABL probe, both of them hybridized to chromosome 9, were demonstrated via fluorescence in situ hybridization (FISH). Furthermore, cohybridization with two differently labeled BCR/ABL translocation DNA probes indicated a BCR/ABL fusion apparently located on 9q34. Molecular studies revealed a rearrangement of the BCR region and expression of a chimeric BCR/ABL mRNA of CML configuration. These findings indicate that the BCR/ABL fusion resulted from an unusual relocation of the BCR gene from its normal position on 22ql I to 9q34 adjacent to the ABL gene.     

Spontaneous splenic rupture in atypical (Philadelphia chromosome negative) chronic myeloid leukaemia following blastic crisis

Philadelphia chromosome negative and bcr/abl negative chronic myeloid leukaemia (CML) is an uncommon atypical CML. We describe a patient with this disorder who experienced an acute blastic transformation that resulted in rapid splenic enlargement and subsequent atraumatic splenic rupture. Clinically, spontaneous splenic rupture may be a difficult diagnosis to make and this case highlights the importance of considering atraumatic splenic rupture as a cause for unexplained abdominal pain in a patient with a haematological malignancy.     

Translocation 3;21 in Philadelphia chromosome positive chronic myeloid leukemia at diagnosis

We describe a further case of Philadelphia chromosome-positive chronic myeloid leukemia with a t(3;21)(q26.2;q22) present in the chronic phase. Blastic transformation occurred 8 months after presentation. The presence of the t(3;21) may indicate a poor prognosis.     

A new translocation in chronic myeloid leukemia--t(4;9;22)--resulting in a masked Philadelphia chromosome

A patient with chronic myeloid leukemia is described in whom a novel complex translocation was found among chromosomes #4, #9, and #22, resulting in a "masked" Philadelphia chromosome. The breakpoint in chromosome #4 (band q21) is in the same region as the breakpoint seen in the t(4;11), which is associated with some forms of acute leukemia.     

Philadelphia chromosome negative acute lymphoblastic leukemia preceding Philadelphia positive chronic myelogenous leukemia

A patient with Philadelphia chromosome (Ph) negative acute lymphoblastic leukemia (ALL, FAB type L1) developed Ph-positive chronic myelogenous leukemia (CML) after more than 2 years in complete remission. Subsequently, Ph-positive lymphoblastic transformation occurred, which was again successfully treated. Thereafter, the CML state was interrupted twice more by blast crisis. The additional chromosomal abnormalities were atypical for Ph-positive CML. The course is interpreted as a possible example of the multistep development of CML. Blastic transformation occurring prior to the Ph chromosome has been reported in only two cases previously.     

Cytogenetic and molecular changes in chronic B-cell leukemia

Cytogenetic studies using B-cell mitogens indicate that approximately 50% of patients with chronic B-cell leukemia (CLL) have chromosome abnormalities. The most common abnormality is an additional chromosome 12, either as the sole abnormality or in conjunction with other abnormalities such as 14q+, 6q-, and 11q-. In two instances, the 14q+ is a result of a translocation from either chromosome 11, t(11;14), or chromosome 19, t(14;19). These two translocations led to the identification of the bcl-1 and bcl-3 genes located on chromosomes 11 and 19, respectively. Very few instances of oncogene activation have been described and it does not seem to be an important mechanism in the pathogenesis of CLL. Further cytogenetic and molecular studies may provide clues for the identification of the genes involved in CLL.