"Masked" philadelphia chromosome (Ph1) due to an unusual translocation

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.

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.

The Philadelphia chromosome: a model of cancer and molecular cytogenetics

Recent developments in molecular biology related to the Ph chromosome lead us to an evaluation of knowledge regarding this chromosome. The molecular advances are related to two cellular oncogenes, c-abl and c-sis, and also to the identification and molecular cloning of specific areas of DNA (e.g., band 22q11), permitting the isolation of a probe specific for the translocation breakpoint domain. In the preponderant number of cases examined, it was found that the breakpoints at 22q11 occur within a limited region of up to 5-6 kb, for which the term "breakpoint cluster region" (bcr) has been suggested. In contrast, breaks at 9q34 seem to occur within a much larger region at the molecular level. Yet to be established is the exact genetic composition of the bcr and a determination as to whether or not the breaks leading to the disease occur preferentially within specific areas. In spite of this level of knowledge, we do not understand how the Ph chromosome participates in CML. If Ph-positive CML is ultimately associated with a cascade of gene activations, the unraveling of their nature and chronology will undoubtedly tell us much of their contribution to the biology of CML, in particular, and to neoplasia, in general. In this respect, the rather clear description of CML in cytogenetic, clinical, and laboratory terms, the relatively long chronic phase of the disease, and the association of the blastic phase with nonrandom chromosome changes (at least in the initial phases of the disease) make Ph-positive CML an excellent candidate for a model for the study of molecular events in human neoplasia.

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.

Translocations (4p+; 6q-) and (12q-; Xp+) in blastic phase of a Ph1-positive chronic myeloid leukemia

This paper reports a 28-year-old woman with Philadelphia chromosome (Ph1)-positive chronic myeloid leukemia (CML) who developed two marrow cell lines during the blastic phase: one with the translocation (12;X) (q 11;p22) and the other with the translocation (4;6) (p 16;q 25). The literature on involvement of chromosomes 12 and X in translocations and the appearance of 6 q- aberration in CML is summarized. The relationship between the 6 q-aberration and the blast cells with lymphoid appearance in the plastic phase of CML is discussed.

Coexistence of cells with unmasked and masked Ph1 in a case of chronic myeloid leukemia in blastic phase

Bone marrow from a patient with chronic myeloid leukemia in blastic phase at diagnosis showed cells with t(9;22), as well as others with a 22q+ marker. The marker was due to t(8;22), and consequently, these cells presented a masked Ph1: t(8;9;22) (q24.2;q34;q11). The marrow contained a wide variety of abnormal clones, which formed an evolutionary pedigree. The pedigree allowed location of the stage of evolution at which masking of the Ph1 had taken place.

Chronic myelogenous leukemia and genetic events at 9q34

Assessment of cytogenetic patterns associated with chronic myelogenous leukemia (CML) suggests that genetic events at band q34 of chromosome nine are critical in the conversion of benign to malignant hematopoiesis. A break at this band is identified in almost all cases of Philadelphia chromosome (Ph1) positive CML, is also noted in some cases of Ph1 negative CML and cannot be excluded in the remaining cases. The human cellular homolog of the Abelson retrovirus oncogene (c-abl) is situated at band 9q34 and is translocated with the genetic sequences distal to the break point at this site in Ph1 positive disease. This oncogene has been shown experimentally to transform pre-B cells and it is expressed in primitive cells of the granulocytic series which are involved in CML. Although the break in CML chromosomes at 9q34 and the location of c-abl at 9q34 could be unrelated, it seems more likely that the two genetic events are associated with evolution of malignant hematopoiesis of man.

Masked Philadelphia chromosome caused by translocation (9;11;22)

In a patient with chronic myelocytic leukemia (CML), chromosome analysis revealed a translocation involving chromosomes No. 9, 11, and 22, with three break points, thus giving origin to a so-called "masked" Philadelphia chromosome (Ph1). A review of similar cases reported in the literature indicates that a masked Ph1 is very rare, that the chromosomes involved vary from case to case, and that in most cases the pattern of the rearrangement is quite different from that of two- and three-chromosome variant Ph1 translocations.

Hereditary adenomatosis of the colon and rectum: relevance to cancer promotion and cancer control in humans

We propose that SF derived from normal-appearing biopsies of ACR gene carriers exist in an initiated state as the result of a dominant mutation. Based on our studies with the ACR cell system, we further suggest that, although an initiated state is essential to cancer development, not all initiated cells necessarily develop into cancerous cells. The genetic makeup of an initiated cell has been established through linkage between abnormal phenotypic markers and pedigree profiles and through cell hybridization, including initial analysis of gene products. We believe that it is consistent with an autosomal dominant trait. In contrast, cells from patients who are homozygous for chromosomal breakage syndromes, including those with xeroderma pigmentosum, represent an experiment of nature which presumably underlies factors associated with cancer promotion in humans. We have demonstrated that ACR cells can be differentially transformed by oncogenic viruses, a carcinogen (MNNG), and gamma-ray irradiation, and that they can proliferate in vitro after exposure to a tumor promoter (TPA. This simple experimental model provides a novel system for the study of tumor promotion in vitro. We further suggest that, through the use of TPA, various stages associated with cancer development in humans, i.e., initiation through promotion and progression, can be identified in vitro. Attempts to apply these results in vivo are currently in progress. The apparent susceptibility of ACR cells to further transformation by oncogenic viruses and chemical and physical agents indicates that genetic information residing within these cells, probably in the form of a relatively limited and specific number of DNA sequences associated with the ACR mutation, renders them more sensitive to these three distinct classes of carcinogens. We submit that, through our tests on SF, and ACR gene carriers within recognized ACR clusters can be diagnosed at present with sufficient certainty to warrant immediate action. In addition, it seems that the time has arrived for a major undertaking to screen for persons who are likely to be at increased risk of cancer, perhaps through walk-in clinics. An underlying assumption in these studies is that predisposition to cancer, in general, is associated with an autosomal dominant trait in obligatory heterozygote gene carriers.