A hidden Philadelphia chromosome

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.

Four cases with complex Philadelphia translocations, including one with appearance de novo of a "masked" Ph

Four cases of chronic myelogenous leukemia (CML) with complex Philadelphia (Ph) translocations are described. The first case was that of a 50-year-old woman in the chronic phase of CML. Her leukemic cells showed a complex Ph translocation involving chromosomes #9, #11, and #22 [i.e., t(9;9;22;11)(11qter----11q11::9q11----9q34:: 9p11----9pter;22qter----22q11::9q34?;11 pter----11q11::22q11----22qter)]. In addition to the complex Ph translocation, the leukemic cells contained del(10)(p13). The second case was that of a 21-year-old man whose leukemic cells contained a translocation involving chromosomes #5, #9, and #22 [i.e., t(5;22;9)(q31;q11;q34)], resulting in a "masked" Ph chromosome. The third case was that of a 37-year-old man whose leukemic cells had a complex Ph translocation involving chromosomes #8, #9, and #22 [i.e., t(8;9;22)(q13;q34;q11)]. The fourth patient was a 41-year-old woman diagnosed as having CML in myeloid blastic phase, at which time the first specimen was examined by us. This blood sample showed a karyotype of 45,XX, -9, -17, -22, +mar1, +mar2,9q+. No Ph chromosome was present. A standard Ph translocation was detected in the cells obtained from the spleen, when the patient underwent splenectomy for treatment of the blastic crisis. Subsequent specimens obtained from the blood and bone marrow showed that the leukemic cells contained three clones: 45,XX, -9, -17, -22, +mar1, +mar2,9q+/46,XX, -17, +mar1,t(9;22)(q34;q11)/46,XX,t(9;22)(q34;q11). Cells with the "masked" Ph chromosome were thought to have been derived from the clone with the standard Ph translocation. We postulate that some variant Ph translocations, including those with a "masked" Ph chromosome, may be generated by a stepwise process following the genesis of a standard Ph translocation.

Genomic diversity of Philadelphia-positive chronic myelogenous leukemia

The incidence of breakpoints in CML patients with variant translocations was investigated. There was no relationship between the length of various chromosomes with breakpoint frequency. However, a significantly higher (p less than 0.05) incidence of breaks were seen on the long arms as compared to the short arms due mainly to the involvement of 9q and 22q in these translocations. Chromosome 17 showed a significantly (p less than 0.005) higher involvement in these translocations, however only when 9q34-qter was not cytogenetically involved. A total of 683 breaks were found in 225 cases. 362 of these were located at c-abl and c-sis, while 110 were at other oncogenetic sites. The prognostic and hematologic features of patients with variant translocations are not significantly different from those of CML cases with the typical 9q;22q translocation. Some of these complex translocation, where the breakpoints are correlated with oncogenetic sites, are further discussed in molecular terms.

Different break-points in Philadelphia chromosome variant translocations and in constitutional and sporadic translocations

Three different samples of translocations were considered in an attempt to identify those chromosomal bands preferentially involved in variant Philadelphia chromosome (Ph1) translocations, and to compare them with bands preferentially broken in constitutional and sporadic translocations. The first sample included 204 cases of variant Ph1 translocations with 221 identified break-points (bp), the second consisted of 106 cases of non-Robertsonian constitutional translocations with 213 bp identified, and the third one of 185 bp identified in sporadic translocations found occasionally in single cells of subjects with normal karyotypes and without haematological disorders. A statistical analysis demonstrated that there are some bands preferentially broken in each of the samples, and this with a high level of significance (P less than 0.001). The analysis of the distributions of the chi 2 components permitted us to identify the 12 bands preferentially involved in variant Ph1 translocations and the 13 and 9 bands preferentially involved in constitutional and sporadic translocations, respectively. The comparison among the groups of preferential bp showed that the bands most involved in the three samples are different. Some theoretical problems related to the origin of the Ph1 chromosome are discussed.

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.

"Masked" Ph1-chromosome in chronic myelogenous leukaemia (CML)

The CML patients with so called masked Ph1-chromosome have been reviewed. Although the importance of c-sis and c-abl oncogenes is gaining popularity yet their role in the genesis of CML remain obscure. Patients with masked Ph1-chromosomes where chromosome 9 is not involved in the translocation(s) will provide a clue to the role of c-abl and/or c-sis in oncogenesis.

Application of cytogenetics in neoplastic diseases

This review will concern itself with the application of cytogenetic findings in neoplastic diseases. This application can be divided into two general categories: practical and theoretical. The practical applications reside in utilizing karyotypic changes, particularly in leukemias and lymphomas, not only for diagnostic purposes but also for predicting response to therapy and prognosis. This is especially evident in the various acute nonlymphocytic leukemias and in most of the acute lymphoblastic leukemias. Thus, a definite correlation exists between the cytogenetic findings and the various clinical, laboratory, and cytologic parameters of most of the leukemias. Undoubtedly, these leukemias will ultimately be classified and defined more in terms of their cytogenetic aspects than any other. Though the application in lymphoma is not at the same level as that in leukemia, developments in that field certainly indicate a similar utilization of the cytogenetic findings in these diseases. The presence or absence of a Ph1 chromosome in a chronic myelocytic leukemia has been utilized widely, not only in the diagnosis but also in the predictability of response; the cytogenetic findings have also been utilized in predicting the blastic phase of disease. The list of specific chromosome changes in various solid tumors is of a lesser number, but significant developments indicate that the applicability of chromosome changes in these diseases will, also, be established in the near future. The application of chromosome findings to theoretical aspects of malignancy has assumed an important place recently in the demonstration that so-called oncogenes (or proto-oncogenes) are located or associated with areas of human chromosomes in which breaks and translocations are involved. Thus, it appears that chromosome changes in human malignancy, once their specificity is established, are important parameters in the clinical and theoretical aspects of the disease. A discussion will also be given on primary vs. secondary chromosome changes and their significance in the biology and behavior of the malignancy.

The Philadelphia (Ph) chromosome in leukemia. II. Variant Ph translocations in acute lymphoblastic leukemia

Nearly 20 patients with a masked Philadelphia (Ph) translocation have been described in chronic myelocytic leukemia. We report two instances of acute lymphoblastic leukemia (ALL) with variant Ph translocations. One case, involving a 26-year-old male, was associated with a variant t(14;22)(q32;q11) translocation. The second case involved a 36-year-old male with a more complex translocation, t(9;15;22)(q12;q26;q11). In each case, cells with a masked Ph translocation were observed. These appear to be the first ALL cases reported with a masked Ph chromosome. The findings are discussed in relation to recent knowledge regarding the genesis of the Ph chromosome.