Trisomy 8 as sole karyotypic aberration in an ovarian metastasizing Sertoli-Leydig cell tumor

Sertoli-Leydig cell tumors (SLCTs) represent a rare group of sex-cord stromal tumors of the ovary of unknown pathogenesis. We report a SLCT of intermediate differentiation with peritoneal recurrence and lymph node metastasis 12 months after removal, including cytogenetic analysis by comparative genomic hybridization and fluorescence in situ hybridization, which showed trisomy 8 as sole unbalanced karyotypic aberration. Our results provide evidence that a simple numeric chromosomal abnormality in SLCT may be associated with a malignant phenotype and suggest that the molecular pathogenesis of SLCT may be different from ovarian granulosa-stromal cell tumors.     

Detection of extra chromosomes 12 by fluorescent in situ hybridization (FISH) in ovarian stromal tumors. Study of 12 cases and review of the literature

Chromosomic aberrations play a major role in the initiation and the progression of benign as well as malignant tumors. In particular, trisomy 12 is frequently observed in female genitourinary tract tumors and constitutes a recurrent and often unique anomaly in stromal ovarian tumors such as fibrothecomas. Today, the genetic analysis of fresh or fixed solid tumors is enabled by the fluorescent in situ hybridization method (FISH). Using FISH and/or conventional cytogenetics, we analysed 12 ovarian stromal tumors (6 fibromas, 3 fibro thecomas and 3 thecomas). All of these tumors were benign and trisomy 12 was observed in all cases. Moreover, 3 cases presented trisomy and tetrasomy for chromosome 12 simultaneously. The high frequency of trisomy 12 in this tumor type suggests that this abnormality might be implicated in ovarian tumorigenesis.     

Characteristic pattern of genetic aberrations in ovarian granulosa cell tumors.

The cytogenetic abnormalities of granulosa cell tumors (GCT) of the ovary are only partially known. Up to now, mainly numerical chromosomal aberrations have been described. Therefore we performed a comprehensive study on paraffin-embedded material of 20 GCT (17 adult, 3 juvenile; patient age between 16 and 78 y) combining comparative genomic hybridization (CGH); fluorescence in situ hybridization (FISH) using DNA-specific probes for chromosome 12, 17, 22, and X; DNA cytometry; and immunohistochemistry (inhibin, p53, Ki67). By DNA cytometry, 16 of 20 tumors (80%) were diploid. However, 6 of 16 diploid tumors (37%) showed aberrations by FISH. FISH revealed monosomy 22 in 8/18 cases (40%); trisomy 12 in 5/20 (25%); monosomy X in 2/20 (10%); and loss of chromosome 17 in one case (5%). The main findings by CGH were gains of chromosomes 12 (6 cases, 33%) and 14 (6 cases, 33%) and losses of chromosomes 22 (7 cases, 35%) and X (1 case, 5%), mostly comprising whole chromosomes or chromosome arms. Inhibin and p53 were expressed in 100% and 95% of the tumors, respectively. The Ki67 index ranged from 0% to 61%. Neither immunohistochemistry, nor DNA cytometry and molecular genetic analysis, provided statistically significant prognostic information. In summary, our study reveals a distinctive pattern of cytogenetic alterations in GCT. Our observations confirm earlier reports that trisomy 12 and 14 are frequent aberrations; however, monosomy 22 seemingly is even more prevalent.     

Tetrasomy 12 in ovarian tumors of thecoma-fibroma group: A fluorescence in situ hybridization analysis using paraffin sections

Recent cytogenetical studies have indicated that trisomy 12 is a feature of ovarian tumors in the thecoma-fibroma group. Ten cases of these ovarian tumors were studied in total, including two thecomas, two fibrothecomas, four fibromas, one cellular fibroma and one fibrosarcoma, to clarify the relationship between polysomy 12 and proliferative activity in these tumors. Each formalin-fixed, paraffin-embedded tumor tissue was examined by fluorescence in situ hybridization to determine copy numbers of chromosome 12 and by immunohistochemical staining of Ki-67 for evaluation of tumor cell proliferation. Gains of trisomy 12 were found in seven of the 10 cases, and the percentage of cells with tetrasomy 12, but not that of cells with trisomy 12, was significantly and positively correlated with percentage of Ki-67-positive cells, but significantly and inversely correlated with patient age. These findings suggest that tetrasomy 12 is an age-related aberration of chromosome 12 in ovarian tumors of the thecoma-fibroma group, and that such tumors exhibit more active proliferation in younger patients.     

E-cadherin nuclear staining is useful for the diagnosis of ovarian adult granulosa cell tumor

We recently have demonstrated nuclear localization of E-cadherin in ovarian adult granulosa cell tumors (Histopathology 2011;58:423). The purpose of the present study is to investigate the diagnostic utility of E-cadherin nuclear staining for the differential diagnosis between ovarian adult granulosa cell tumor and its morphological mimics. Tissue samples taken from 81 ovarian tumors and 20 extraovarian tumors were immunohistochemically stained using monoclonal anti-E-cadherin antibody recognizing cytoplasmic domain (clone 36 supplied by BD Biosciences, San Jose, CA). The ovarian tumors consisted of 30 adult granulosa cell tumors, 3 Sertoli-stromal cell tumors, 14 fibrothecomas, 5 carcinoid tumors, 1 large cell neuroendocrine carcinoma, 18 endometrioid adenocarcinomas, and 10 poorly differentiated serous adenocarcinomas. Extraovarian tumors consisted of 16 uterine endometrial stromal neoplasms and 4 pulmonary small cell carcinomas. Only tumor cells with nuclear staining were considered positive in this study. Ninety percent of adult granulosa cell tumors, 67% of Sertoli-stromal cell tumors, 64% of fibrothecomas, 75% of endometrial stromal neoplasms, 75% of small cell carcinomas, and the one large cell neuroendocrine carcinoma showed E-cadherin nuclear expression, whereas all the ovarian carcinoid tumors, endometrioid adenocarcinomas, and poorly differentiated serous adenocarcinomas were negative. E-cadherin nuclear staining is useful in distinguishing between adult granulosa cell tumors and ovarian adenocarcinomas or carcinoid tumors. However, it is of limited use for distinguishing between adult granulosa cell tumors and endometrial stromal neoplasms or small cell carcinomas. E-cadherin should be included in the immunohistochemical panel for an accurate diagnosis of ovarian adult granulosa cell tumors.     

Trisomy 12 in pediatric granulosa-stromal cell tumors. Demonstration by a modified method of fluorescence in situ hybridization on paraffin-embedded material.

The use of fluorescence in situ hybridization (FISH) to detect chromosomal abnormalities has many applications. Use of FISH on archival, paraffin-embedded material has been limited to microscopic sections. We have carried out FISH on preparations of disaggregated nuclei obtained from paraffin-embedded tissue to evaluate chromosome 12 copy number in granulosa-stromal cell neoplasms occurring in infants, children, and adolescents. Trisomy 12 was detected in the majority of cells from three of four juvenile granulosa cell tumors (three ovarian and one testicular) and one malignant granulosa cell tumor. Tetrasomy 12 was observed in a case of ovarian thecoma.     

Trisomies 8 and 20 characterize a subgroup of benign fibrous lesions arising in both soft tissue and bone

Trisomy 8 and trisomy 20 are nonrandom aberrations in desmoid tumors. The presence of these trisomies in related benign fibrous lesions of bone has not been previously addressed. In this study, 22 specimens from 19 patients diagnosed with desmoid tumor, desmoplastic fibroma, periosteal desmoid tumor, osteofibrous dysplasia, or fibrous dysplasia were examined by cytogenetic analysis of short-term cultures and bi-color fluorescence in situ hybridization of cytological touch preparations or paraffin-embedded tissue with centromeric probes for chromosomes 8 and 20. Trisomy 8 and trisomy 20 were detected by molecular cytogenetic methodologies in 15 specimens, including 10 primary bone lesions. Traditional cytogenetic analysis revealed trisomy 8 in two cases of osteofibrous dysplasia. Our findings demonstrate that trisomy 8 and trisomy 20 are also nonrandom aberrations in histologically similar, but clinically distinct, benign fibrous lesions of bone.     

Near-Diploid karyotypes with recurrent chromosome abnormalities characterize early-stage endometrial cancer

Cytogenetic investigation was attempted on 15 endometrial tumors. Whenever possible, a combination of direct harvesting and short-term culture (with or without prior methotrexate synchronization) was used. The analysis was successful in 13 cases: 12 carcinomas of stage I and one atypical hyperplasia. Clonal abnormalities were found in 10 tumors, whereas the remaining three showed a normal karyotype. The modal chromosome number was near-diploid. The abnormal karyotypes contained relatively simple numerical or structural aberrations in all but one tumor, a serous papillary carcinoma with multiple complex changes as well as cytogenetic evidence of intratumor heterogeneity. Gain of 1q, trisomy for chromosomes 2, 7, 10 (this trisomy was shown by in situ hybridization to be present also in a large number of interphase cells), and 12, and loss of chromosome 22 were recurrent aberrations; these are also the cytogenetic anomalies that have been consistently associated with endometrial carcinomas in previous studies. The utilization of both direct harvesting and short-term culture in several cases increased the frequency with which abnormal karyotypes were found; sometimes aberrations were found by the first method but not by the other, and vice versa. Never were different clonal anomalies found by the two approaches in the same case. Synchronization of the cultures generally led to chromosome preparations with more mitoses and of better quality. Again, no different anomalies were found in synchronized and standard cultures from the same tumor.     

Cytogenetic findings and clinical course in a consecutive series of Wilms tumors

Wilms tumor (WT) is characterized by a nonrandom pattern of chromosome aberrations, but the clinical significance of different cytogenetic patterns is unknown. The present study describes the cytogenetic findings and the clinical course in a cohort of 39 children with WT. Samples for short-term culturing and cytogenetic analysis were obtained during a 15-year period. Clonal chromosome aberrations were detected in 23 samples from 19 patients. Tumors that relapsed more often showed clonal aberrations than did tumors that did not. However, this association my have been due to sampling bias. Among the cases with karyotypically abnormal samples, the modal chromosome number was in the near-diploid range in 10, hyperdiploid/hypotriploid in 8, and hypodiploid in 1. The most common changes were trisomy 12 and gain of 1q material (8 cases each), trisomy/tetrasomy 8 (7 cases), and trisomy 13 (5 cases). None of these frequently occurring abnormalities, or the ploidy level, showed any association with clinical outcome, using tumor relapse as an end-point. Nor could any relationship between cytogenetic features and histopathologic subtype be discerned. Although the number of informative cases was too small for proper evaluation, the present study did not contradict the previous notion that loss of material from the long arm of chromosome 16 is associated with poor clinical outcome. All three patients with deletion of 16q developed metastases.     

Cytogenetic evaluation of a large series of hepatoblastomas: numerical abnormalities with recurring aberrations involving 1q12-q21

Hepatoblastoma is a malignant embryonal liver tumor that occurs almost exclusively in infants and very young children. Previous cytogenetic studies of hepatoblastoma have investigated small series or individual cases. This report is on the cytogenetics of a large series of 111 hepatoblastoma specimens, with cytogenetic results consecutively karyotyped over a 12-year period. Abnormal karyotypes were observed in 55 cases (approximately 50% of the total). Numerical aberrations were observed in 41 cases (36% of the total), particularly trisomies of chromosomes 2, 8, and 20. Chromosome losses were less common than chromosome gains. Structural abnormalities were observed in 43 cases (39% of the total). Unbalanced translocations resulting in trisomy 1q and involving breakpoints at 1q12-21 were the most common structural abnormality, observed in 20 tumors (18% of total cases); the corresponding translocated chromosome was highly varied. The previously reported t(1;4) was observed in seven cases. Most tumors with translocations involving 1q12-21 also displayed numerical chromosome aberrations, the most common of which were chromosomal trisomies, whereas tumors with other structural rearrangements had fewer numerical abnormalities.     

Numerical chromosomal aberrations in papillary renal cortical tumors: relationship with histopathologic features

Previous studies have indicated that a combined trisomy of chromosomes 7 and 17 is a constant finding in papillary renal cortical adenomas and that papillary renal cell carcinomas are marked by additional trisomies such as trisomy 12, 16, and 20. The aim of our study was to compare this cytogenetic classification of papillary renal cortical tumors with conventional histopathologic classification. We performed interphase cytogenetics with enumeration probes for chromosomes 7, 12, 16, 17, and 20 on 41 papillary tumors found in 21 nephrectomy and 10 autopsy kidneys. A total of 38 tumors harbored gains of chromosomes 7 or 17, and most of these showed a trisomic signal distribution. The three tumors with normal copy numbers for chromosomes 7 and 17 were a papillary grade-2 carcinoma, a small adenoma (both with distinctive oxyphilic cytoplasm), and a papillary carcinoma with focally clear cells. Gains for chromosomes 12, 16, or 20 were found in 21 tumors and were significantly associated with the presence of histologic criteria of malignancy ( P<0.0001). Histopathologic and cytogenetic features of malignancy were found in eight tumors smaller than 10 mm. There is a good agreement of cytogenetic and histopathologic criteria of malignancy in papillary renal cell tumors. Interphase cytogenetics might give useful additional information in cases of doubt or when only small biopsy specimens are available.     

The influence of cytogenetic aberrations on gene replication in chronic lymphocytic leukemia patients

Chronic lymphocytic leukemia (CLL) is the most common leukemia in humans, with the major cytogenetic aberrations of trisomy 12 and deletion of 13q14. This study examined the influence of these aberrations on general gene replication. The study group included three subgroups: (1) 15 CLL patients, (2) 4 CLL patients with trisomy 12, (3) 3 CLL patients with deletions in 13q14. Five healthy individuals served as a control group. Monocolor fluorescence in situ hybridization (FISH) with probes for c-myc, HER-2/neu, and p53 was applied to lymphocyte nuclei for the evaluation of replication timing. Asynchronous replication (SD) rate was significantly higher in all CLL patients (P < 0.01) when compared to the control group and was even higher in the group of CLL patients with trisomy 12 and 13q14 deletion (P < 0.01). The asynchrony rate was significantly higher in cells with trisomy 12 for all three probes analyzed, compared to "healthy" cells in the same patients (P < 0.001). To conclude, in CLL patients with a chromosomal aberration such as trisomy 12 and 13q14 deletion we were able to demonstrate a high rate of asynchrony of replication. The high correlation between cells with trisomy 12 and SD pattern could reflect direct influence of the aberration on gene replication and cell cycle control.     

The STK11/LKB1 Peutz-Jegher gene is not involved in the pathogenesis of sporadic sex cord-stromal tumors, although loss of heterozygosity at 19p13.3 indicates other gene alteration in these tumors

Germ line mutations in the STK11/LKB1 tumor-suppressor gene (chromosome 19p13.3) are responsible for the Peutz-Jeghers syndrome (PJS). PJS patients frequently develop neoplasms of various organs. Ovarian sex cord-stromal tumor (SCST) with annular tubules, which shows a characteristic morphology intermediate between granulosa cell and Sertoli cell tumors, is distinctively associated with PJS. Although somatic mutations of STK11 are reportedly rare in sporadic forms of common cancers linked to PJS, there are no available studies assessing STK11 alterations in larger series of sporadic ovarian tumors with granulosa, Sertoli or combined differentiation. We examined 29 sporadic SCSTs for loss of heterozygosity (LOH) at 19p13.3, mutation, and promoter methylation of STK11. LOH at 19p13.3 was detected in 12 of 29 (41%) SCSTs, with the highest frequency at chromosome marker D19S894, which localizes approximately 3 mb centromeric to STK11, and it was more frequent in granulosa/Sertoli-stromal cell tumors (10 of 19; 52%) than in thecoma-fibroma tumors (2 of 10; 20%). The 2 fibrothecomas harboring LOH contained sex cord elements. None of the LOH-positive SCSTs demonstrated mutations or promoter methylation of STK11. Our results indicate that LOH at 19p13.3 in sporadic SCSTs targets a gene different from STK11, and may play a role in the pathogenesis of sporadic SCSTs, especially in tumors containing sex cord derivatives.     

Cytogenetics of agnogenic myeloid metaplasia: a study of 61 patients

Agnogenic myeloid metaplasia (AMM) or idiopathic myelofibrosis is a chronic myeloproliferative disorder characterized by fibrotic bone marrow, extramedullar haematopoiesis, and a leukoerythroblastic picture in circulating blood. The cytogenetic data on AMM are scanty and no recurring chromosome abnormality has been associated with the natural course of this disease. Trisomy 1q, del(13q), del(20q), and trisomy 8, appear in about two thirds of patients with demonstrable chromosome aberrations. We report on the cytogenetic analyses of 61 consecutive patients with AMM studied at diagnosis. The metaphases could not be found in 10/61 (16.4%) patients, and chromosome studies were successful in 51 patients. Twenty-one patients (41%) had an abnormal clone, whereas 30 (59%) patients had a normal karyotype. Most frequent pathological findings included trisomy 8 (either alone or within a complex karyotype) in five patients, aberrations of chromosome 12 (translocation in two, monosomy in two, and trisomy in one patient), and aberrations of chromosome 20 (interstitial deletion in two, monosomy in two, and trisomy in one patient). We also detected aberrations of chromosome 13 (translocation in two and an interstitial deletion and trisomy in one patient each) and chromosome 18 (derivative 18 in two patients and a monosomy and deletion in one patient each). Three patients exhibited complex aberrations involving several chromosomes, sometimes with a mosaicisam. A near-tetraploid karyotype was observed in a single patient. Balanced translocations [t(2;16)(q31;q24), t(5;13)(q13;q32), t(12;13)(p12;q13), and t(12;16)(q24;q24)] were present in four patients. While the series of patients studied displayed chromosomal aberrations that are frequently observed in AMM, we found some new abnormalities (balanced translocations and polyploidy) that are rarely observed in AMM.     

Chromosome aberrations in B-cell chronic lymphocytic leukemia: reassessment based on molecular cytogenetic analysis

In B-cell chronic lymphocytic leukemia (B-CLL) clonal chromosome aberrations are detected in approximately 40–50% of tumors when using conventional chromosome banding analysis. Most studies find trisomy 12 to be the most frequent chromosome aberration, followed by structural aberrations of the long arm of chromosomes 13 and 14. Trisomy 12 and the ”14q+” marker are associated with shorter survival times, while the patients with 13q abnormalities have a favorable outcome, similar to those with a normal karyotype. The development of molecular cytogenetic techniques has greatly improved our ability to detect chromosome aberrations in tumor cells. Using fluorescence in situ hybridization, chromosome aberrations can be detected not only in dividing cells but also in interphase nuclei, an approach referred to as interphase cytogenetics. The prevalence of specific aberrations in B-CLL is currently being reassessed by interphase cytogenetics. By far the most frequent abnormality are deletions involving chromosome band 13q14, followed by deletions of the genomic region 11q22.3-q23.1, trisomy 12, deletions of 6q21-q23, and deletions/mutations of the TP53 tumor suppressor gene at 17p13. The evaluation of the true incidence of these aberrations now provides the basis for more accurate correlations with clinical characteristics and outcome. Deletions/mutations of the TP53 gene have been shown to be associated with resistance to treatment and to be an independent marker for poor survival. 11q deletions have been associated with extensive nodal involvement, rapid disease progression, and short survival times. Whether trisomy 12, 13q14, and 6q deletions have a prognostic impact awaits further study. The application of these molecular cytogenetic techniques will also contribute to the identification of the pathogenetically relevant genes that are affected by the chromosome aberrations in B-CLL. Received: 2 February 1998 / Accepted: 31 March 1998     

On the significance of trisomy 7 and sex chromosome loss in renal cell carcinoma

Cytogenetic analysis of 30 renal cell carcinomas showed 3p aberrations in nine tumors, trisomy 7 in 17 tumors, and clonal loss of one sex chromosome in 14 tumors. The 3p aberrations and trisomy 7 were present in the same clone in two tumors and in separate clones in three tumors. Loss of one sex chromosome was present together with 3p aberrations in the same clone in one tumor and occurred in seemingly unrelated clones in two tumors. It occurred as the sole change in five tumors. Clones with trisomy 7 as the only change were present in six tumors. Trisomy 7 and loss of one sex chromosome were present in separate clones in four tumors and in the same clone in one tumor. Because +7 and -X/-Y were thus rarely present together with clonal structural abnormalities, in particular 3p changes, our findings make it highly unlikely that loss of one sex chromosome or trisomy 7 represents a primary change in renal cell carcinoma. We instead suggest that there is a tendency for normal kidney cells to lose an X or a Y chromosome and also to gain an extra copy of chromosome 7. This tendency is retained by renal carcinoma cells; therefore, trisomy 7 and sex chromosome loss should not be viewed as tumor-specific abnormalities in this context. Whether these simple numerical aberrations reflect in vivo mosaicism or are acquired in vitro remains unresolved.     

Trisomy 8 in primary esthesioneuroblastoma.

Esthesioneuroblastoma is a rare malignancy believed to be derived from neuroectodermal stem cells within the olfactory epithelium. We have obtained the karyotype of a primary esthesioneuroblastoma following brief (7-day) in vitro culture, and have determined that the only observable cytogenetic anomaly is the presence of an additional chromosome 8. Previously, the karyotypes of two cell lines established from metastatic esthesioneuroblastomas have been reported to contain the equivalent of three copies of chromosome 8, in addition to other chromosomal aberrations, including the reciprocal translocation, t(11;22)(q24;q12). Examination of the cytogenetic literature suggests that an extra copy of chromosome 8 is a common occurrence in undifferentiated small round cell tumors frequently observed to carry the t(11;22), including esthesioneuroblastoma, Ewing's sarcoma, peripheral neuroepithelioma, Askin's tumor, and rhabdomyosarcoma. These data, combined with our report of a small round cell tumor with the karyotype 47,XY, +8, indicate that trisomy 8 may be a common phenomenon in these tumors, and may also provide some sort of selective advantage to these tumor types.     

Cytogenetic aberrations in 188 benign and borderline adipose tissue tumors

Chromosome studies of lipomas have revealed an extensive cytogenetic heterogeneity. To investigate the frequencies of previously recognized cytogenetic subgroups and to find out if more recurrent rearrangements can be identified, we have analyzed cytogenetically short-term tissue cultures of 237 samples from 188 adipose tissue tumors obtained from 142 patients. Only one of 58 tumors from 18 patients with multiple lipomas (more than two tumors) had karyotypic changes. Among the sporadic lipomas, 20 tumors had supernumerary ring chromosomes of unknown origin, 55 had different aberrations involving chromosome segment 12q13-15, 11 had changes of 6p or chromosome 13, but no rings or 12q13-15 changes, and 14 had various other aberrations. Ring chromosomes were found in all cytogenetically abnormal lipomas histologically classified as atypical and in nine tumors classified as typical lipoma or spindle cell lipoma. Recombinations between 12q 13-15 and a few other bands or segments were seen more than once: 3q27-28 (15 tumors), 2p22-24 and 2q35 (four tumors), 1 p32-34 and 13q 12-14 (three tumors), and 5q33 (two tumors). Recombinations of 12q 13-15 with 2q35 and 13q 12-14 have not been described before. Of eight tumors with chromosome 13 aberrations, five had loss of 13q material. Aberrations of 12q 13-15, 6p, and/or chromosome 13 were found simultaneously in nine tumors. Two to four samples from the same tumor were investigated in 29 tumors with clonal aberrations. Thirteen of these tumors displayed clonal evolution, also noted in another 17 tumors in which only one sample had been investigated. Thus clonal evolution occurred in 30% of the tumors and was particularly frequent in atypical lipomas. Genes Chrom Cancer 9:207-215 (1994). © 1994 Wiley-Liss, Inc.     

Cytogenetic analysis of invasive breast cancer: a study of 27 Asian patients

Tumor cytogenetic analysis from 27 patients with breast cancer diagnosed at the Singapore General Hospital revealed complex karyotypic aberrations in 12 cases. The study group comprised 25 women and 2 men, ranging in age from 33 to 78 years (median 52 years). Ethnic distribution consisted of 22 Chinese, 3 Malaysian, and 2 Indian patients. Pathologic assessment disclosed 24 invasive ductal, 2 invasive mucinous, and 1 mixed invasive mucinous and ductal carcinomas. Histologic grading showed 3 grade 1, 10 grade 2, and 12 grade 3 tumors; 2 cancers were not graded, because they had been subjected to prior chemotherapy. Tumor sizes ranged from 1.5 to 10 cm (median 3 cm). Eleven cases were axillary node negative, whereas the remaining 16 node-positive cancers affected as many as 3 nodes in 8 cases and 4 or more nodes in another 8. Twenty cases demonstrated estrogen-receptor positivity, and 8 cases progesterone-receptor positivity. The spectrum of cytogenetic abnormalities involved chromosomes 1, 3, 6, 7, 8, 11, 16, and 17 and ranged from gains and deletions of both long and short arms, trisomy, monosomy, and other rearrangements. There was a trend toward the presence of karyotypic abnormalities in tumors of higher grade.