Incidence of numerical chromosome aberrations in meningioma tumors as revealed by fluorescence in situ hybridization using 10 chromosome-specific probes

OBJECTIVE: Although information on the cytogenetic characteristics of meningioma tumors has accumulated progressively over the past few decades, information on the genetic heterogeneity of meningiomas is still scanty. The aim of the present study was to analyze by interphase fluorescence in situ hybridization (FISH) the incidence of numerical abnormalities for chromosomes 1, 9, 10, 11, 14, 15, 17, 22, X, and Y in a group of 70 consecutive meningioma tumors. Another goal was to establish the potential associations among the altered chromosomes, as a way to assess both intertumoral and intratumoral heterogeneity. METHODS: For the purpose of the study, 70 patients diagnosed with meningioma were analyzed. Interphase FISH for the detection of numerical abnormalities for chromosomes 1, 9, 10, 11, 14, 15, 17, 22, X, and Y was applied to fresh tumor samples from each of the patients studied. RESULTS: The overall incidence of numerical abnormalities was 76%. Chromosome Y in males and chromosome 22 in the whole series were the most common abnormalities (46% and 61%, respectively). Despite the finding that monosomy of chromosome 22/22q(-) deletions are the most frequent individual abnormality (53%), we have observed that chromosome gains are significantly more common than chromosome losses (60% versus 40%). Chromosome gains corresponded to abnormalities of chromosomes 1 (27%), 9 (25%), 10 (23%), 11 (22%), 14 (33%), 15 (22%), 17 (23%), and X in females (35%) and males (23%) whereas chromosome losses apart from chromosome 22 frequently involved chromosomes 14 (19%), X in males (23%), and Y in males (32%). Although an association was found among most gained chromosomes on one side and chromosome losses on the other side, different association patterns were observed. Furthermore, in the latter group, monosomy 22/22q(-) was associated with monosomy X in females and monosomy 14/14q(-) was associated with nulisomy Y in males. In addition, chromosome losses usually involved a large proportion of the tumor cells whereas chromosome gains were restricted to small tumor cell clones, including tetraploid cells. CONCLUSIONS: Our results show that meningiomas are genetically heterogeneous tumors that display different patterns of numerical chromosome changes, as assessed by interphase FISH.     

Genomic imbalances in 61 renal cancers from the proximal tubulus detected by comparative genomic hybridization

Comparative genomic hybridization (CGH) has been applied to characterize 61 primary renal cell carcinomas derived histogenetically from the proximal tubulus. The tumor samples comprised 46 clear-cell renal cell carcinomas (ccRCCs) and 15 papillary renal cell carcinomas (pRCCs). Changes in the copy number of entire chromosomes or subregions were detected in 56 tumors (92%). In ccRCCs, losses of chromosome 3 or 3p (63%); 14q (30%); 9 (26%); 1 and 6 or 6q (17% each); 4 and 8 or 8p (15% each); 22 (11%); 2 or 2q and 19 (9% each); 7q, 10, 16, 17p, 18, and Y (7% each); and 5, 11, 13, 15, and 21 (4% each) were detected. Most frequent genomic gains in ccRCC were found on chromosome 5 (63%); 7 (35%); 1 or 1q (33%); 2q (24%); 8 or 8q, 12, and 20 (20% each); 3q (17%); 16 (15%); 19 (13%); 6 and 17 or 17q (11% each); and 4, 10, 11, 21, and Y (9% each). In pRCCs, gains in the copy number of chromosomes 7 and 17 (7/15, each) and 16 and 20 (6/15, each) were frequent. One pRCC showed amplification of subchromosome regions 2q22-->q33, 16q, 17q and the entire X chromosome. In pRCC, losses were less frequently seen than gains. Losses of chromosomes 1, 14, 15, and Y (3/15 each) and 2, 4, 6, and 13 (2/15 each) were observed. In ccRCCs, statistical evaluation revealed significant correlations of chromosomal imbalances with tumor stage and grade, i.e., a gain in copy number of chromosome 5 correlated positively with low tumor grade, whereas a gain of chromosomes 10 and 17 correlated positively with high tumor grade. Furthermore, loss of chromosome 4 correlated positively with high tumor stage.     

Karyotype pecularities of human colorectal adenocarcinomas

Summary The data of the chromosome abnormalities in 15 colorectal tumors are presented. Rearrangements of the short arm of chromosome 17, leading to deletions of this arm or its part were noted in 12 tumors; in 2 other cases, one of the homologs of pair 17 was lost. The losses of at least one homolog of other chromosomal pairs were also found: chromosome 18, in 12 out of 13 cases with fully identified numerical abnormalities; chromosome 5, in 6 tumors; chromosome 21, in 5 cases; chromosomes 4, 15, and 22, in 4 cases each. Additional homologs of pair 20 were observed in 6 tumors, extra 8q was found in 5 tumors, and extra 13q in 6 cases. Rearrangements of the short arm of chromosome 1 and the long arm of chromosome 11 characterized 6 tumors each. The data recorded in our series differ from the data of other authors in two respects: the high incidence of the loss of sex chromosomes and the rearrangements of the long arm of chromosome 9. X chromosomes were missing in 4 out of 7 tumors in females, and Y chromosomes were absent in 5 out of 8 tumors in males. The long arm of chromosome 9 was rearranged in 8 cases, in 5 of them the breakpoint being at 9q22. Cytological manifestations of gene amplification (double minutes or multiple microchromosomes) were noted in 6 tumors.     

Chromosomal alterations in 98 endometrioid adenocarcinomas analyzed with comparative genomic hybridization

The aim of the present study was to investigate chromosomal alterations in a large set of homogeneous tumors, 98 endometrioid adenocarcinomas. We also wanted to evaluate differences in chromosomal alterations in the different groups of tumors in relation to stage, survival and invasive or metastatic properties of the tumors. Comparative genomic hybridization (CGH) was used to detect chromosomal alterations in tissue samples from 98 endometrioid adenocarcinomas. All chromosomes were involved in DNA copy number variations at least once in the tumor material, but certain changes were recurrent and rather specific. Among the specific changes, it was possible to identify 39 chromosomal regions displaying frequent DNA copy number alterations. The most frequent alteration was detected at 1q25-->q42, in which gains were found in 30 cases (30%). Gains at 19pter-->p13.1 were detected in 26 tumors (26%) and at 19q13.1-->q13.3 in 19 tumors (19%). Increased copy numbers were also detected at 8q (8q21-->q22 and 8q22-->qter), at a relatively high rate, in 17 cases (17%). Furthermore, gains at 10q21-->q23 and 10p were found in 14 (14%) and 13 cases (13%), respectively. The most common losses were found in the three regions 4q22-->qter, 16q21-->qter and 18q21-->qter, all of which were detected in eight of the 98 tumors (8%). We also detected differences between the tumors from deceased patients and from survivors. Gain at 1q25-->q42 was more commonly detected in the tumors from patients who died of cancer. We noted that the regions most affected differed in the different surgical stages (I-IV). The results of the CGH analysis identify specific chromosomal regions affected by copy number changes, appropriate objects for further genetic studies.     

Delineation and physical separation of novel translocation breakpoints on chromosome 1p in two genetically closely associated childhood tumors

Sporadic childhood tumors associated with Beckwith-Wiedemann syndrome (BWS) all show abnormalities of the same region on chromosome 11. In addition to chromosome 11, other chromosome regions are affected in some of these tumor types. In this study we analyzed the region on chromosome 1p involved in the etiology of BWS-associated tumors, Wilms tumor, rhabdomyosarcoma, and hepatoblastoma. For this purpose we determined the location of two novel translocation breakpoints in this chromosome region in cells from a Wilms tumor and cells from a rhabdomyosarcoma. We constructed a map of the region and found that both breakpoints are separated by at least 875 kb. We identified a PAC clone which crosses the rhabdomyosarcoma breakpoint and found several exons within this clone. We established that this breakpoint is located proximal to the PAX7 gene and, therefore, identified a new region involved in the etiology of rhabdomyosarcomas.     

Molecular cytogenetic characterization of pancreas cancer cell lines reveals high complexity chromosomal alterations

Karyotype analysis can provide clues to significant genes involved in the genesis and growth of pancreas cancer. The genome of pancreas cancer is complex, and G-band analysis cannot resolve many of the karyotypic abnormalities seen. We studied the karyotypes of 15 recently established cell lines using molecular cytogenetic tools. Comparative genomic hybridization (CGH) analysis of all 15 lines identified genomic gains of 3q, 8q, 11q, 17q, and chromosome 20 in nine or more cell lines. CGH confirmed frequent loss of chromosome 18, 17p, 6q, and 8p. 14/15 cell lines demonstrated loss of chromosome 18q, either by loss of a copy of chromosome 18 (n = 5), all of 18q (n = 7) or portions of 18q (n = 2). Multicolor FISH (Spectral Karyotyping, or SKY) of 11 lines identified many complex structural chromosomal aberrations. 93 structurally abnormal chromosomes were evaluated, for which SKY added new information to 67. Several potentially site-specific recurrent rearrangements were observed. Chromosome region 18q11.2 was recurrently involved in nine cell lines, including formation of derivative chromosomes 18 from a t(18;22) (three cell lines), t(17;18) (two cell lines), and t(12;18), t(15;18), t(18;20), and ins(6;18) (one cell line each). To further define the breakpoints involved on chromosome 18, YACs from the 18q11.2 region, spanning approximately 8 Mb, were used to perform targeted FISH analyses of these lines. We found significant heterogeneity in the breakpoints despite their G-band similarity, including multiple independent regions of loss proximal to the already identified loss of DPC4 at 18q21.     

A specific chromosomal abnormality in rhabdomyosarcoma

A specific chromosomal abnormality, t(2;13)(q35;q14), was discovered in five cases of advanced rhabdomyosarcoma. It was identified directly in cells that had metastasized from bone marrow in one patient and in xenografts derived from the tumors of four other patients. The translocation was not restricted by histologic subtype, but was found in cases classified as alveolar, undifferentiated, or embryonal. Cytogenetic hallmarks of gene amplification (double minute chromosomes and homogeneously staining regions) were apparent in three cases. Other frequent abnormalities included rearrangements of chromosomes lp and trisomy of chromosome 8. The absence of the t(2;13) in more than 100 cases of other pediatric solid tumors investigated in our laboratory indicates its specificity for rhabdomyosarcoma. These cytogenetic findings suggest directions for further investigation of the molecular events underlying the genesis of this tumor.     

Numerical chromosomal changes in DNA hypodiploid solid tumors: restricted loss and gain of certain chromosomes.

BACKGROUND: DNA hypodiploidy is a unique and rare finding associated with aggressive behavior in solid tumors. Identifying the chromosomal changes underlying this feature may provide important information on the development and progression of these neoplasms. METHODS: Fluorescence in situ hybridization analysis using alpha-satellite probes for nine autosomes and the two sex chromosomes was performed on interphase cells from 27 solid tumors which had been shown to be DNA hypodiploid by flow cytometry. The chromosomal abnormalities were correlated with the DNA index and tumor subtypes. RESULTS: The data show mutually exclusive loss of certain chromosomes and compensatory gain of other chromosomes in different tumors. The net loss was slightly more than the net gain for the chromosomes tested. Polysomy of chromosome 7 and monosomy of chromosomes 17, X and loss Y were found in most tumors. Significant differential loss of chromosomes 6,10, and 12 among DNA hypodiploid breast, kidney and lung carcinomas was noted. CONCLUSIONS: Our study shows (i) gain of chromosome 7 and loss chromosome 17 in most DNA hypodiploid tumors, (ii) specific chromosomal loss was noted in breast and renal cell carcinomas, and (iii) that different mechanisms for DNA hypodiploid and hyperdiploid development may exist.     

At least four different chromosomal regions are involved in loss of heterozygosity in human breast carcinoma

Three chromosome regions, i.e., 11p15, 13q, and 17p, were previously reported by three independent groups to be specifically reduced to hemizygosity in human primary breast cancer. We examined the DNA of 64 mammary tumors for loss of heterozygosity (LOH) with 28 polymorphic DNA markers dispersed on 10 arms of 8 different chromosomes. Complete or near-complete absence of LOH was observed on 5 arms (5 chromosomes). LOH at all three previously invoked regions was confirmed, and the highest frequency was found on 17p (67% of heterozygous patients). Allele loss of a marker from chromosome 3 (region p14-p21) was found in 7 of 15 informative cases. Concurrent LOH at 2 to 4 loci was noted in 20 of the 43 tumors showing LOH. Allele losses did not correlate with any of the six clinico-histopathological variables investigated, but in a group of patients in which we were unable to demonstrate LOH, the absence of distant metastases was statistically significant (P less than 0.05). These results suggest that some of the observed allele losses reflect random events, possibly as a result of genetic instability, but are not without biological significance for the progression of particular subclasses of breast tumors.     

Characterization of supernumerary rings and giant marker chromosomes in well-differentiated lipomatous tumors by a combination of G-banding,CGH, M-FISH,and chromosome- and locus-specific FISH

Supernumerary ring chromosomes and/or giant marker chromosomes are often seen in soft-tissue tumors of low-grade or borderline malignancy, such as well-differentiated liposarcomas or atypical lipomas. Classic cytogenetic banding techniques have proved insufficient to identify the genomic composition and structure of such rings and markers, but fluorescent in situ hybridization (FISH) studies have shown that they consist mainly of amplified material from chromosome 12, more specifically from bands 12q13-->q15. We have used the new FISH-based screening techniques comparative genomic hybridization (CGH) and multicolor-FISH (M-FISH) in combination with G-banding and analysis by chromosome- and locus-specific fluorescent in situ probes to examine in detail the karyotypic characteristics of 22 lipomatous tumors, most of them classified histologically as well-differentiated liposarcomas, selected because they had been shown to harbor rings and/or marker chromosomes. M-FISH, in contrast to G- banding, was found to be informative with regard to the chromosomal origin of the rings and other markers present, whereas CGH and hybridizations with locus-specific probes helped identify which subchromosomal regions were involved. We found that chromosome bands 12q15-->q21 were always gained, with 12q15-->q21 being amplified (i.e., a green-to-red ratio >2 by CGH) in 14 of 22 tumors. In three tumors, two distinct but close amplicons in 12q could be identified, corresponding to bands 12q13-->q15 and 12q21. The genomic segment 1q21-->q23 was gained in 12 cases, reaching the level of amplification in seven. Bands 6q24 and 7p15, whose pathogenetic involvement in liposarcomas has not been reported previously, were gained in three cases each. In addition, the rings and giant markers often contained interspersed sequences from several other chromosomes that did not give an equally clear impression of being nonrandomly involved.     

Detection of chromosome aberrations in paraffin sections of seven gonadal yolk sac tumors of childhood

Yolk sac tumors are the most frequent kind of malignant pediatric germ cell tumor and may have a fundamentally different pathogenesis than adult germ cell tumors. Since few cytogenetic studies have been performed so far, in situ hybridization was applied to interphase cell nuclei of seven gonadal yolk sac tumors of childhood in routine paraffin-embedded tissue sections. The panel of chromosome-specific DNA probes was selected on the basis of their relevance in adult germ cell tumors and consisted of five DNA probes specific for the (peri)centromeric regions of chromosomes 1, 8, 12, 17 and/or X and/ or one DNA probe specific for the subtelomeric region of chromosome 1 (p36.3). As in adult germ cell tumors, all pediatric gonadal yolk sac tumors had an increased incidence of numerical chromosome aberrations. All tumors showed an overrepresentation of at least three chromosomes. Gains of chromosome 12, which is highly specific in adult germ cell tumors, were diagnosed in six pediatric gonadal yolk sac tumors. The DNA indices determined in the paraffin-embedded tumor material correlated well with the in situ hybridization findings. A chromosome was either over- or underrepresented, compared with the corresponding DNA indices, in only a few cases. The short arm of chromosome 1 in adult germ cell tumors is often involved in structural aberrations. In pediatric germ cell tumors, the short arm of chromosome 1 is also a nonrandom site of structural aberrations. Moreover, the presence of a deletion at 1p36.3 in four out of five tumors suggests that the loss of gene(s) in this region is an important event in the pathogenesis of gonadal yolk sac tumors of childhood.     

Linkage studies with 17q and 18q markers in a breast/ovarian cancer family.

Genes on chromosomes 17q and 18q have been shown to code for putative tumor suppressors. By a combination of allele-loss studies on sporadic ovarian carcinomas and linkage analysis on a breast/ovarian cancer family, we have investigated the involvement of such genes in these diseases. Allele loss occurred in sporadic tumors from both chromosome 17p, in 18/26 (69%) cases, and chromosome 17q, in 15/22 (68%) cases. In the three familial tumors studied, allele loss also occurred on chromosome 17 (in 2/3 cases for 17p markers and in 2/2 cases for a 17q allele). Allele loss on chromosome 18q, at the DCC (deleted in colorectal carcinomas) locus, was not as common (6/16 cases [38%]) in sporadic ovarian tumors but had occurred in all three familial tumors. The results of linkage analysis on the breast/ovarian cancer family suggested linkage between the disease locus and 17q markers, with a maximum lod score of 1.507 obtained with Mfd188 (D17S579) polymorphism at 5% recombination. The maximum lod score for DCC was 0.323 at 0.1% recombination. In this family our results are consistent with a predisposing gene for breast/ovarian cancer being located at chromosome 17q21.     

Karyotypic rearrangements in 20 uterine leiomyomas

Short-term cultures from 106 uterine leiomyomas have been cytogenetically investigated. In 29 cases the number of metaphases was insufficient for analysis. A normal female karyotype was found in 57 tumors and clonal chromosome rearrangements in 20. A reciprocal translocation, t(12;14) (q14----q15;q23----q24), was observed in 10 tumors and probably represents a primary change of tumorigenic importance. In four of the tumors containing this specific anomaly, secondary chromosome changes were also present. The 10 karyotypically abnormal leiomyomas without a t(12;14) had various structural and numerical aberrations involving chromosomes 1, 2, 3, 4, 6, 8, 9, 10, 11, 12, 13, and 19. Different structural changes of chromosome 1 were the second most frequent abnormalities, being found in five tumors. Ring chromosomes were observed in three cases, but never as the sole change.     

Genomic profiling maps loss of heterozygosity and defines the timing and stage dependence of epigenetic and genetic events in Wilms' tumors

To understand genetic and epigenetic pathways in Wilms' tumors, we carried out a genome scan for loss of heterozygosity (LOH) using Affymetrix 10K single nucleotide polymorphism (SNP) chips and supplemented the data with karyotype information. To score loss of imprinting (LOI) of the IGF2 gene, we assessed DNA methylation of the H19 5' differentially methylated region (DMR). Few chromosomal regions other than band 11p13 (WT1) were lost in Wilms' tumors from Denys-Drash and Wilms' tumor-aniridia syndromes, whereas sporadic Wilms' tumors showed LOH of several regions, most frequently 11p15 but also 1p, 4q, 7p, 11q, 14q, 16q, and 17p. LOI was common in the sporadic Wilms' tumors but absent in the syndromic cases. The SNP chips identified novel centers of LOH in the sporadic tumors, including a 2.4-Mb minimal region on chromosome 4q24-q25. Losses of chromosomes 1p, 14q, 16q, and 17p were more common in tumors presenting at an advanced stage; 11p15 LOH was seen at all stages, whereas LOI was associated with early-stage presentation. Wilms' tumors with LOI often completely lacked LOH in the genome-wide analysis, and in some tumors with concomitant 16q LOH and LOI, the loss of chromosome 16q was mosaic, whereas the H19 DMR methylation was complete. These findings confirm molecular differences between sporadic and syndromic Wilms' tumors, define regions of recurrent LOH, and indicate that gain of methylation at the H19 DMR is an early event in Wilms' tumorigenesis that is independent of chromosomal losses. The data further suggest a biological difference between sporadic Wilms' tumors with and without LOI.     

Amplification at 9p in cervical carcinoma by comparative genomic hybridization.

DNA copy number changes were studied by comparative genomic hybridization on 10 tumor specimens of squamous cell carcinoma of cervix obtained from Korean patients. DNA was extracted from paraffin-embedded sections after removal of non-malignant cells by microdissection technique. Copy number changes were found in 8/10 tumors. The most frequent changes were chromosome 19 gains (n=6) and losses on chromosomes 4 (n=4), 5 (n=3), and 3p (n=3). A novel finding was amplification in chromosome arm 9p21-pter in 2 cases. Gains in 1, 3q, 5p, 6p, 8q, 16p, 17, and 20q and losses at 2q, 6q, 8p, 9q, 10p, 11, 13, 16q, and 18q were observed in at least one of the cases.     

Gene copy number changes in dermatofibrosarcoma protuberans - a fine-resolution study using array comparative genomic hybridization

Dermatofibrosarcoma protuberans (DFSP) is a rare, slow-growing, low-grade dermal tumor. Cytogenetic and FISH studies have revealed that the chromosomal rearrangements characteristic of DFSP tumors involve both translocations and the formation of a supernumerary ring derived from chromosomes 17 and 22. The t(17;22) (q22;q13.1) translocation generates a gene fusion between COL1A1 and PDGFB, which serves as a diagnostic marker of DFSP. In the present study we performed array-CGH (aCGH) analysis on ten DFSP tumors. The COL1A1 region at 17q was gained in 71% (5/7) of the samples and the PDGFB region at 22q was gained in 43% (3/7) of the individual samples. In addition to the 17q and 22q gains, altogether 17 minimal common regions of gain and one region of loss were detected.     

Loss of heterozygosity and K-ras gene mutations in gastric cancer

In order to identify relevant genetic lesions in gastric carcinoma, we searched for tumor suppressor gene inactivation and K-ras gene mutations by analyzing tumor and control DNAs from 34 patients. These were from an epidemiologically defined area of Italy characterized by one of the world's highest incidences of stomach cancer. Allele losses were investigated by the Southern blotting procedure at 16 polymorphic loci on 11 different chromosomes. Our data demonstrate that chromosomal regions 5q, 11p, 17p and 18q are frequently deleted, and that 7q and 13q chromosome arms are also involved, although at a lower frequency. Loss of heterozygosity (LOH) at region 11p was not found during other surveys carried out on patients of different geographic origins. No specific combination of allelic losses could be recognized in the samples analyzed, the only exception being that tumors with 17p allelic loss also showed LOH on the 18q region. When matching frequent LOH events and the stage of progression of the tumors, we observed a trend of association between advanced stages and allelic losses on 17p and 18q chromosome arms. The analysis of K-ras, carried out by the polymerase chain reaction and denaturing gradient gel electrophoresis, demonstrated transforming mutations in only 3 out of 32 cases. Colorectal tumorigenesis proceeds by the accumulation of genetic alterations, including K-ras mutations and inactivation of tumor suppressor genes on the 5q, 17p and 18q regions. Our data indicate that, although gastric and colorectal neoplasias share common genetic alterations, they probably progress through different pathways.     

Association between genetic subgroups of pancreatic ductal adenocarcinoma defined by high density 500 K SNP-arrays and tumor histopathology

The specific genes and genetic pathways associated with pancreatic ductal adenocarcinoma are still largely unknown partially due to the low resolution of the techniques applied so far to their study. Here we used high-density 500 K single nucleotide polymorphism (SNP)-arrays to define those chromosomal regions which most commonly harbour copy number (CN) alterations and loss of heterozygozity (LOH) in a series of 20 PDAC tumors and we correlated the corresponding genetic profiles with the most relevant clinical and histopathological features of the disease. Overall our results showed that primary PDAC frequently display (>70%) extensive gains of chromosomes 1q, 7q, 8q and 20q, together with losses of chromosomes 1p, 9p, 12q, 17p and 18q, such chromosomal regions harboring multiple cancer- and PDAC-associated genes. Interestingly, these alterations clustered into two distinct genetic profiles characterized by gains of the 2q14.2, 3q22.1, 5q32, 10q26.13, 10q26.3, 11q13.1, 11q13.3, 11q13.4, 16q24.1, 16q24.3, 22q13.1, 22q13.31 and 22q13.32 chromosomal regions (group 1; n = 9) versus gains at 1q21.1 and losses of the 1p36.11, 6q25.2, 9p22.1, 9p24.3, 17p13.3 and Xp22.33 chromosomal regions (group 2; n = 11). From the clinical and histopathological point of view, group 1 cases were associated with smaller and well/moderately-differentiated grade I/II PDAC tumors, whereas and group 2 PDAC displayed a larger size and they mainly consisted of poorly-differentiated grade III carcinomas. These findings confirm the cytogenetic complexity and heterogenity of PDAC and provide evidence for the association between tumor cytogenetics and its histopathological features. In addition, we also show that the altered regions identified harbor multiple cancer associate genes that deserve further investigation to determine their relevance in the pathogenesis of PDAC.     

Similar chromosomal abnormalities in several retinoblastomas

Summary The study of banded chromosomes of nine sporadic unilateral retinoblastomas revealed near diploid karyotypes with multiple numerical and (or) structural abnormalities in all tumors. An identical marker i(6p) was noted in cells of the modal class of six retinoblastomas. Extra copies of the short arm of chromosome 6 were observed in seven tumors: +i(6p) in 6 and +6q- in one. Less regular but repeated findings were a loss of one sex chromosome, and markers 1p+ and 17q+. The structure of these markers was not identical in different tumors. Abnormalities of chromosome 13 were not observed in tumor cells, nor in blood lymphocytes stimulated by PHA.     

A detailed analysis of chromosomal changes in heritable and non-heritable retinoblastoma

Summary Full cytogenetic analysis of 27 different retinoblastoma tumors is presented. Gross aneuploidy of chromosome arms 6p and 1q were very common, being observed in 15/27 and 21/27 tumors, respectively. However, we found that chromosome 13 was rarely missing: only 3/27 had a detectable monosomy affecting 13q14. Monosomy of chromosome 13 by small deletion or rearrangement was also not observed in any of 12 retinoblastoma tumor lines analyzed detail at the 300–400 chromosome band level. A novel observation in retinoblastoma was the discovery of non-random translocations at three specific breakpoints, 14q32 (4/12), 17p12 (5/12), and 10q25 (3/12). Genomic rearrangements similar to those described involving C-myc in Burkitt lymphoma 14q+ cells could not be demonstrated in the four 14q+ retinoblastoma lines using molecular techniques, and a probe mapping to the site implicated to have an activating role in lymphoma. These data suggest that there is a target for rearrangement at 14q32 but it is not the same sequence used in some Burkitt lymphomas. Two other breakpoints (2p24 and 8q24) coincided with the mapped position of cellular oncogenes, but also failed to show a molecular rearrangement with the oncogene probes. The breakpoints, 10q25 and 17p12, are constitutional fragile sites which may predispose these regions to act as acceptors of translocations in malignant cells. One line had double minute chromosomes, and was the only one of 16 (6%) tested with the N-myc probe which had an amplification. Different tumors from single patients with multifocal heritable retinoblastoma showed independent karyotype evolution. Unilateral non-heritable tumors exhibited a high level of karyotype stability throughout both in vivo and in vitro growth. The various common patterns of aneuploidy and translocations probably confer an early selective advantage to malignant cells, rather than induce malignant transformation.