Molecular cytogenetic studies of pediatric ependymomas.

Cytogenetic and molecular studies of ependymomas have previously demonstrated deletions of chromosomes 17 and 22 as frequent abnormalities, implicating inactivation of tumor suppressor genes in the pathogenesis of these tumors. In the present study, we analyzed 22 childhood ependymomas by standard cytogenetic analysis, fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR)-based microsatellite analysis of chromosomes 17 and 22. Microsatellite analysis of chromosome 6 was performed to identify submicroscopic deletions implicated by the cytogenetic studies. Among the 22 cases, we demonstrated loss of chromosome 22 in 2 patients, deletion of chromosome 17 in 2 patients, and rearrangements or deletions of chromosome 6 in 5 patients. These data do not suggest that loss of a gene on chromosome 17p plays a primary role in the initiation of pediatric ependymomas. This is in contrast to what has been reported for pediatric CNS primitive neuroectodermal tumors and malignant astrocytomas, in which deletion of 17p is regarded as a primary event. Furthermore, loss of chromosome 22 may define a subset of ependymomas more commonly seen in adults. Cytogenetic studies in this series, however, suggest that a region on the long arm of chromosome may be involved in the development and/or progression of ependymomas in children.

Isochromosome 17q demonstrated by interphase fluorescence in situ hybridization in primitive neuroectodermal tumors of the central nervous system.

We previously reported an i(17q) as a non-random finding in childhood primitive neuroectodermal tumors (PNETs) of the central nervous system. In the present study, we describe a two-color interphase fluorescence in situ hybridization (FISH) assay for detection of chromosome 17 abnormalities in tumors. Thirty-four PNETs were analyzed by FISH with a series of chromosome 17-specific probes which map to 17p13.3-17q25. The results from the FISH assay were then compared to the karyotypes prepared from the tumors. Ten of the 34 cases demonstrated an i(17q) by FISH and standard cytogenetics. Two PNETs were shown to have an i(17q) by FISH alone, and three additional tumors had deletions of 17p. Thus, a total of 15 of 34 (44%) of the PNETs in this series had a deletion of 17p. This study confirms and extends our previous reports that an i(17q) is the most common cytogenetic abnormality in PNETs. The interphase FISH assay which we employed will have clinical utility for diagnosis of children with malignant brain tumors, and it may be used for identification of tumors with 17p deletions for molecular studies aimed at identifying disease genes.

Enhanced MYCN expression and isochromosome 17q in pineoblastoma cell lines.

We have established two cell lines, PER-452 and PER-453, from an 8-month-old girl with an extensive pineoblastoma. Characterization of these lines revealed that the proto-oncogenes MYC and MYCN were not amplified, but both cell lines showed MYCN expression comparable to a cell line with 200-fold MYCN amplification. Both cell lines contained an i(17q). These results support the concept that pineoblastomas belong to a larger group of primitive neuroectodermal tumors of the central nervous system. These two cell lines provide a unique opportunity to investigate the molecular genetic mechanisms underlying these neoplasms further.

Abnormalities of chromosome 22 in pediatric meningiomas.

Cytogenetic studies of eight meningiomas in young children or adolescents were performed. Two tumors exhibited normal karyotypes. Two tumors from patients with bilateral acoustic neurofibromatosis demonstrated monosomy 22 as the only abnormality. Four patients had more complicated karyotypes in which one or both of the chromosomes 22 were missing or structurally altered. The most common secondary changes in these four tumors involved monosomy or structural abnormalities of chromosome 6. These findings confirm that the primary cytogenetic changes in meningioma are similar in children and adults. Molecular analyses of pediatric meningiomas with deletions or translocations of chromosome 22 will be useful for identifying the role of chromosome 22 tumor suppressor genes in this disease.

46,XX,15p+ documented as dup (17p) by fluorescence in situ hybridization.

We report on a patient with a complex heart defect, short webbed neck, multiple other minor features, and a 46,XX,15p+ de novo karyotype. The enlarged short arm of the chromosome 15 was Distamycin-DAPI and C-band negative. Fluorescence in situ hybridization (FISH) using an alpha satellite probe from chromosome 15 demonstrated hybridization only to the normal 15. In situ hybridization using a set of probes that bind to the short arm (17p13) and centromere of chromosome 17 demonstrated that the extra material on chromosome 15, including the centromere, was derived from chromosome 17. Therefore, this patient has a duplication of the centromere and short arm of chromosome 17. Clinical manifestations in this patient were consistent with those in previously described patients with dup (17p).

Cytogenetics of melanocytic tumors.

Chromosome studies of human melanocytic tumors have demonstrated non-random karyotypic abnormalities of chromosomes 1, 6, 7, 9, and 10. These visible genetic alterations may provide clues to the location of oncogenes and suppressor genes involved in the development of lesions from benign nervus to metastatic melanoma, and to the mechanisms by which the function of these genes is altered. To date, however, none of the specific growth regulatory genes important in this neoplastic progression has been identified, with the possible exception of the erbB oncogene in the later stages. Recent results in other human tumors do suggest, however, that the combined cytogenetic and molecular genetic approach will soon lead to the recognition of a number of important genes, both inherited and somatically altered, and that significant clinical applications will follow.

Molecular analysis of a partial deletion of 22q in a central nervous system rhabdoid tumor.

We previously reported the non-random occurrence of monosomy 22 in rhabdoid or atypical teratoid tumors of the brain in three young children. We now present cytogenetic and molecular studies of an additional rhabdoid tumor with the karyotype 46,XX,-9,-22,+i(1q),+der(22)t(9;22)(p13;q11)/45,XX,-9,-10,- 22,+i(1q),+der(22)t(9;22)(p13;q11). These studies further demonstrate the involvement of chromosome 22, and they begin to define the critical region containing a gene or genes involved in the development or progression of rhabdoid tumors of the brain.

Malignant fibrous histiocytoma of the brain in a six-year-old girl.

We have prepared karyotypes from a malignant fibrous histiocytoma (MFH) of the brain of a 6-year-old girl. Sporadic cases of MFH in the central nervous system have been reported. However, to our knowledge, this is the first central nervous system tumor to be subjected to cytogenetic analysis. The tumor demonstrated a complex karyotype, with a variety of numerical and structural abnormalities. Although no specific cytogenetic abnormality was observed, the karyotype of this case was similar to those reported for adult MFH of soft tissues.

Chromosomal translocation t(1;13)(p36;q14) in a case of rhabdomyosarcoma.

Cytogenetic studies of a rhabdomyosarcoma of mixed embryonal and alveolar histology in an 11-month-old male revealed a single structural abnormality, t(1;13)(p36;q14). This abnormality may define a subset of patients with a variant of the t(2;13)(q35;q14) translocation frequently seen in alveolar rhabdomyosarcoma.

Possible involvement of the chromosome region 10q24----q26 in early stages of melanocytic neoplasia.

A recent report described a translocation involving 10q24 in a compound nevus. We have examined our series of melanocytic tumors ranging from common nevi to metastatic melanomas with the following results. In 24 nevi (congenital or common acquired), no karyotypically abnormal clones were found. Two of 10 dysplastic nevi had abnormal clones: one had an unidentified marker chromosome, the other had a t(9;10)(p24;q24) translocation. Of the three complex primary melanomas studied (lesions with both radial and vertical growth phase present), one had a t(10;?)(q26;?) and one showed a loss of chromosome 10. Among 51 advanced melanomas (primary and metastatic), all but one had multiple alterations, and 18 of these had lost one or more copies of chromosome 10. The one invasive melanoma without multiple abnormalities had a complex three-way rearrangement: 46,XY,t(5;6;10) with breakpoints on chromosome 10 at both q23 and q25. These data support the view that the terminal region of 10q may harbor one or more genes involved in the early stages of melanocytic neoplasia.

Structural alteration in the MYB protooncogene and deletion within the gene encoding alpha-type protein kinase C in human melanoma cell lines.

A correlative study was done to determine possible relationships between nonrandom aberrations in chromosomes 1, 6, and 7 occurring in human cutaneous malignant melanoma and the structure of oncogenes as well as specific genes encoding growth factors and growth factor receptors. Thirty cell lines derived from primary or metastatic melanomas of 28 patients were analyzed by Southern blotting with nick-translated probes for 28 different genes, some of which map near frequent chromosomal breakpoints observed in melanoma. An alteration in the MYB protooncogene was observed in a cell line derived from a primary melanoma in the vertical growth phase, which correlated with a 6q22 chromosomal abnormality. Another primary melanoma cell line had a cytogenetically undetected tumor-specific deletion within the gene for alpha-type protein kinase C. Polymorphic alleles for the genes encoding the epidermal growth factor receptor and alpha-type protein kinase C were also observed.

A t(1;19) chromosome translocation in three cases of human malignant melanoma.

Abnormalities of chromosome 1, including trisomy for all or a portion of the long arm, have been frequently reported in many cancers. Anomalies of chromosome 19 are far less common, although a t(1;19)(q23;p13) translocation has been reported in association with pre-B-cell leukemia. We have observed a t(1;19)(q12;p13) translocation in three cases of advanced melanoma, with the translocation chromosome representing an extra dose of 1q in each instance. The breakpoint on 1q was within the centromeric heterochromatin, proximal to the site in pre-B-cell leukemia, but the breakpoint on 19p appeared identical. The gene for human insulin receptor has recently been mapped to this region of chromosome 19 (p13.2-13.3). This gene shares structural and sequence homologies with the epidermal growth factor receptor (erb-B oncogene) and members of the src family of oncogenes, suggesting that alterations in the insulin receptor, resulting from chromosomal translocation, could lead to a role in tumorigenesis. The present findings may permit this possibility to be examined in a neoplasm of neuroectodermal origin.