Cytogenetics of tumors of soft tissue and bone. Implication for pathology

Chromosomal organization and localization of the human histone deacetylase 9 gene (HDAC9)

Epigenetically mediated modulation of gene promoter function through histone acetylation modifying enzymes, which regulate the acetylation state of histone proteins and other promoter-bound transcription factors, is increasingly appreciated as a key component in the regulation of reversible gene expression. While histone acetyltransferases (HATs), which are frequently part of multisubunit coactivator complexes, lead to the relaxation of chromatin structure and transcriptional activation, histone deacetylases (HDACs) tend to associate with multisubunit corepressor complexes, which result in chromatin condensation and transcriptional repression of specific target genes. We have isolated and characterized the human HDAC9 genomic sequence, which spans a region of 458 kb and which has one single chromosomal locus. Determination of the exon-intron splice-junctions established that HDAC9 is encoded by 23 exons ranging in size from 22 bp (exon 1) to 264 bp (exon 11). Characterization of the 5' flanking genomic region revealed that the human HDAC9 promoter lacks both the canonical TATA and CCAAT boxes; CpG elements are missing. The human HDAC9 open reading frame is 3036 bp long and encodes a 1011 aa protein with a predictive molecular weight of 111.3 kDa and an isoelectric point of 6.41. Fluorescence in situ hybridization analysis localized the human HDAC9 gene to chromosome 7p21, a region which has been associated particularly with the pathogenesis of gynecological tumors.

Transdifferentiation of neoplastic cells

Transdifferentiation is a process in which a stable cell's phenotype changes to that of a distinctly different cell type. It occurs during certain physiological processes and leads to transition of tumor cell phenotypes. The latter process includes neoplastic epithelial-epithelial transition, neoplastic epithelial-mesenchymal transition, neoplastic mesenchymal-epithelial transition and transition between non-neural and neural neoplastic cell. This phonomenon is exemplified in some origin-debated tumors, such as carcinosarcoma, pleomorphic adenoma, synovial sarcoma, Ewing's/pPNET, and malignant fibrohistiocytoma. We propose that differentiation disturbance of cancer cells should include not only undifferentiation and dedifferentiation, but also transdifferentiation as well. Tumor cell transdifferentiation may be influenced or determined by cellular genetic instabilities, proliferation and apoptosis, as well as by extracellular matrix and growth factors.

Malignant transformation of neurofibromas in neurofibromatosis 1 is associated with CDKN2A/p16 inactivation

Patients with neurofibromatosis 1 (NF1) are predisposed to develop multiple neurofibromas (NFs) and are at risk for transformation of NFs to malignant peripheral nerve sheath tumors (MPNSTs). Little is known, however, about the biological events involved in the malignant transformation of NFs. We examined the CDKN2A/p16 gene and p16 protein in NFs and MPNSTs from patients with NF1. On immunohistochemical analysis, all NFs expressed p16 protein. The MPNSTs, however, were essentially immunonegative for p16, with striking transitions in cases that contained both benign and malignant elements. None of the benign tumors had CDKN2A/p16 deletions, whereas three of six MPNSTs appeared to have homozygous CDKN2A/p16 deletions. Methylation analysis and mutation analysis of CDKN2A/p16 in MPNSTs did not reveal any abnormalities. These results show that malignant transformation of NF is associated with loss of p16 expression, which is often secondary to homozygous deletion of the CDKN2A/p16 gene. The findings suggest that CDKN2A/p16 inactivation occurs during the malignant transformation of NFs in NF1 patients and raises the possibility that p16 immunohistochemistry may provide ancillary information in the distinction of NF from MPNST.

Lipoblastoma: a case with t(7;8)(q31;q13)

Lipoblastoma is a rare benign adipose tumor which, in all of the cases so far described, presents an involvement of chromosome 8 in the region 8q11-13. We hereby report the results of the second case of lipoblastoma studied by fluorescence in situ hybridization (FISH), in a 13-month-old boy. An abnormal karyotype 46,XY,t(7;8)(q31;q13) was found in 90% of the metaphases examined, in agreement with the previously reported observations. We suggest the region 8q11-13 may contain a relevant locus for lipoblastoma origin.

Cytogenetic findings in malignant mixed mesodermal tumors of the uterus

Cytogenetic analyses of four malignant mixed mesodermal tumors (MMMT) of the uterus are reported, of which one was of the homologous type and three of the heterologous. Karyotypic analyses were obtained in two cases from original tumors and in two cases from tumors xenotransplanted into nude mice. The karyotype of the homologous MMMT was normal in three different passages of a nude mice xenograft line established from the primary tumor. The heterologous tumors showed normal karyotype in one case and hyperdiploid and near triploid range with extensive numerical and structural rearrangements in two cases. Deletion of chromosome 1 at p32, and deletion of chromosome 11 at q13 were common markers in anomalous cases. The chromosomes most often involved in structural rearrangements were chromosomes 1, 9, 11, 12, 17, and 19. Double minutes, homogeneously staining regions, and telomeric association were also seen.

Cytogenetic aberrations and DNA ploidy in soft tissue sarcoma. A Southwest Oncology Group Study

We performed cytogenetic analysis and determined DNA content by flow cytometry (FCM) on freshly disaggregated tumor biopsies from 45 patients with soft tissue sarcomas (STS). Cytogenetically aberrant clones characterized 30 (67%) tumors, with the remaining 15 yielding normal karyotypes with or without nonclonal aberrations. No tumors with multiple unrelated clones were observed. Among the 30 tumors with clonally abnormal karyotypes, 21 (70%) had near-diploid stemlines, six were near-triploid and three were near-tetraploid. Ten of the clonally aberrant tumors contained nonrandom chromosomal translocations characteristic of histologic subtypes. Overrepresentation of chromosomes 7 and 8 were common numerical aberrations. Structural aberrations most often involved chromosomes 1, 7, 9, 12, and 14. Clustering of breaks in 9p resulting in partial loss of the short arm was frequent. Unstable aberrations including rings, dicentrics, large markers, small numbers of double minutes, and telomeric associations were seen in nine tumors. With FCM, 27 (60%) tumors had aneuploid DNA content and 18 (40%) were DNA diploid. Of those 18 DNA diploid tumors, 11 showed clonal karyotypic aberrations. In addition, apparent discrepancies between the results of the cytogenetics and FCM with respect to ploidy pattern were seen in 13 samples; 11 had DNA content in the peritriploid to peritetraploid range but the corresponding karyotype was normal or near-diploid. When the findings of the cytogenetics and DNA content analyses were combined, an abnormal cell population by one or both methods was detected in 38 (84%) tumors. The concurrent application of standard cytogenetics and DNA ploidy by FCM provide complementary information confirming a high incidence of genetic alterations in STS.

Ten years of the cytogenetics of soft tissue tumors

Recent cytogenetic and molecular genetic investigations in solid tumors in general, and in soft tissue tumors in particular, have provided us with a wealth of information. We have gained new insights in how tumors may arise, and some soft tissue tumors besides their identification by pathology now also have a genetic identity. This genetic identity is defined by: specific chromosome changes and by molecular changes related to the chromosome anomalies. However, much work remains to be done. In soft tissues as in other solid tumors many tumor types await the first or more extensive chromosome investigation, and in those in which nonrandom, especially simple chromosome changes emerge, molecular studies are to be undertaken starting from the breakpoints. Those tumors that seem to deviate chromosomally or molecularly from the expected, because of already established genetic changes, must be more thoroughly investigated by both pathologists and geneticists. The same accounts for the molecular investigation of chromosomally normal tumors known to show subtypes with specific chromosomal changes: e.g. lipoma, leiomyoma.

Advances in the understanding of the molecular pathology of connective tissue neoplasms

Although primary malignant neoplasms of the connective tissues are uncommon, they have been subjected to intense study by modern molecular and other analytical techniques. Aberrations of genes and their products are providing insight into aetiopathogenesis and indicating improved methods of histopathological diagnosis and patient management.

Gains and losses of DNA sequences in liposarcomas evaluated by comparative genomic hybridization

Comparative genomic hybridization (CGH) was used to detect and map the regions of gain, high-level amplification, and loss of DNA sequences in 14 liposarcomas. Thirteen tumors showed DNA sequence copy number changes of one or more genomic regions (mean, six aberrations/tumor; range, 0-17). These aberrations were observed in almost every chromosome but some chromosomal regions were affected more often than others. DNA sequence gains were more frequent than losses. The most common gain was seen at 12q14-21 (50% of tumors). Other frequent gains (29%) were of 1q21-24, 8cen-q21.2, 19q, and 20q. High-level amplification was observed in six (43%) tumors and included as minimal common segments bands 12q15, 1q22, and 1q24. In five (36%) tumors, sequences at 1q21-24 and 1q32 were found to be gained simultaneously with 12q14-21, which means that in 71% of the tumors with gain at 12q, an increase of DNA sequence copy number at 1q was also observed. The most common losses of DNA sequences (21%) occurred from regions 9p21-pter and 13q21-qter. Most of the aforementioned regions have not previously been reported to be altered in liposarcomas. The detection of a novel recurring amplicon at 1q21-24 with high-level amplification at 1q22 and frequent simultaneous DNA sequence gain at 12q14-21 (high-level amplification at 12q15) suggests that genes linked to both these regions may play a significant role in the development and progression of liposarcomas.

Recent developments in soft tissue tumors

This article reviews the clinicopathological features of several recently described soft tissue tumours, namely ossifying fibromyxoid tumour, angiomyofibroblastoma, epithelioid angiosarcoma, retiform haemangioendothelioma, intra-abdominal desmoplastic small cell tumour, spindle cell liposarcoma and low grade fibromyxoid sarcoma. Conceptual changes are also discussed. These include the relationship between Ewing's sarcoma and peripheral primitive neuroectodermal tumour, the proposed use of the term atypical lipoma for a subset of well differentiated liposarcomas, and the occurrence at a wide variety of sites of inflammatory myofibroblastic lesions of uncertain biological potential. In addition, advances in the study of soft tissue lesions at the molecular and cytogenetic levels are outlined, with particular emphasis on the recent identification of tumour-specific karyotypic abnormalities in a wide variety of sarcomas.