Evidence for alternative lengthening of telomeres in liposarcomas in the absence of ALT-associated PML bodies.

Immortalized and cancer cells maintain their telomeres by activation of a telomere maintenance mechanism (TMM). In approximately 85% of cancers telomerase is activated (TA) but in some tumours, in particular sarcomas, an alternative lengthening of telomeres (ALT) pathway is used. Liposarcomas are the most common soft-tissue sarcoma in adults and they activate ALT or telomerase with equal frequency, however no TMM has been identified in approximately 50% of liposarcomas. In our study, we have shown that instability at the minisatellite MS32, usually associated with ALT activation, aids the identification of liposarcomas that have recombination-like activity at telomeres in absence of ALT associated PML-bodies (APBs). Furthermore, using single molecule telomere analysis, we have detected complex telomere mutations directly in ALT positive liposarcomas and interestingly in some liposarcomas with an unknown TMM but high MS32 instability. We have shown by sequence analysis that some of these complex telomere mutations must arise by an inter-molecular recombination-like process rather than by deletion caused by t-loop excision or by unequal telomere-sister-chromatid-exchange (T-SCE), which is known to be elevated in ALT cell lines. Preliminary evidence also suggests that inter-molecular recombination events may be processed differently in liposarcomas with APBs compared to those without. In conclusion, we have shown for the first time, that some telomerase negative liposarcomas without APBs have other features associated with ALT, indicating that the incidence of ALT in these tumours has previously been under-estimated. This has major implications for the use of cancer treatments targeted at TMMs.

Multiple mechanisms of telomere maintenance exist in liposarcomas.

PURPOSE: Telomeres are specialized nucleoprotein complexes that protect and confer stability upon chromosome ends. Loss of telomere function as a consequence of proliferation-associated sequence attrition results in genome instability, which may facilitate carcinogenesis by generating growth-promoting mutations. However, unlimited cellular proliferation requires the maintenance of telomeric DNA; thus, the majority of tumor cells maintain their telomeres either through the activity of telomerase or via a mechanism known as alternative lengthening of telomeres (ALT). Recent data suggest that constitutive telomere maintenance may not be required in all tumor types. Here we assess the role and requirement of telomere maintenance in liposarcoma. EXPERIMENTAL DESIGN: Tumor samples were analyzed with respect to telomerase activity, telomere length, and the presence of ALT-specific subcellular structures, ALT-associated promyelocytic leukemia nuclear bodies. This multi-assay assessment improved the accuracy of categorization. RESULTS: Our data reveal a significant incidence (24%) of ALT-positive liposarcomas, whereas telomerase is used at a similar frequency (27%). A large number of tumors (49%) do not show characteristics of telomerase or ALT. In addition, telomere length was always shorter in recurrent disease, regardless of the telomere maintenance mechanism. CONCLUSIONS: These results suggest that approximately one half of liposarcomas either employ a novel constitutively active telomere maintenance mechanism or lack such a mechanism. Analysis of recurrent tumors suggests that liposarcomas can develop despite limiting or undetectable activity of a constitutively active telomere maintenance mechanism.

Sarcomas with combined features of liposarcoma and leiomyosarcoma. Study of two cases of an unusual soft-tissue tumor showing dual lineage differentiation.

Two cases are described of a soft-tissue sarcoma characterized histologically by the intimate admixture of areas displaying the features of liposarcoma and leiomyosarcoma. Both cases occurred in men, 70 and 77 years of age. The lesions were located in the left scrotum and abdominal cavity, respectively. Histologically, the lipomatous component in both cases consisted predominantly of well-differentiated liposarcoma with myxoid areas. The smooth-muscle component was characterized by intersecting fascicles of spindle cells displaying nuclear atypicality and scattered mitotic figures; the spindle cells in these areas were strongly immunoreactive with actin and desmin antibodies. The above tumors must be distinguished from angiomyolipoma, spindle-cell lipoma, myolipoma of soft tissue, and more importantly, from "dedifferentiated" liposarcoma. The development of dual lineage differentiation within adipose tissue tumors as exemplified by these two cases may be more prevalent than has been generally recognized, and may require the application of immunohistochemical markers for specific identification of the spindle-cell component.

Liposarcomas. A histogenetic approach to the classification of adipose tissue neoplasms.

A series of atypical lipomas, well-differentiated/dedifferentiated liposarcomas, and myxoid/round cell liposarcomas were examined by light and electron microscopy in order to understand better the marked variation in histologic growth patterns exhibited by adipose tissue neoplasms. We found that they were composed of a mixture of adipocytes and nonfat-storing mesenchymal cells or were predominantly made up of only one of these cell types. From these and other published observations, we feel that 1) myxoid/round cell liposarcomas are composed of adipocytes; 2) spindle cell lipomas, atypical lipomas, and well-differentiated liposarcomas are composed of a mixture of the two cell types; and 3) the dedifferentiated regions of well-differentiated liposarcomas are composed of nonfat-storing mesenchymal cells. The basic structural differences of the two cell types and the quantitative variations when they occur in mixtures seem to account for the marked variations in neoplastic growth patterns.

Benign lipoblastoma and myxoid liposarcoma: a comparative light- and electron-microscopic study.

A benign lipoblastoma and a myxoid liposarcoma were studied by light and electron microscopy. Both of these neoplasms had prominent plexiform vascular networks, early acquisition of fat by vascular pericytes, and progressive accumulation of fat by cells located away from the vasculature. Their component cells had investing basal laminae, pinocytotic vesicles, and cytoplasmic glycogen stores as well as cytoplasmic lipid. The process of neoplastic lipogenesis and the structural features of the neoplastic cells in both neoplasms resembled those of developing non-neoplastic fat tissue. The benign lipoblastoma appears to be analogous to developing fat, while the myxoid liposarcoma appears to recapitulate the actively proliferating zone of developing fat. The relationship between proliferating cells and the plexiform vascular network in all three processes is emphasized. We hypothesize that the vascular pericyte serves as a source for new fat storing cells.

Ultrastructural distinctions between adult pleomorphic rhabdomyosarcomas, pleomorphic liposarcomas, and pleomorphic malignant fibrous histiocytomas.

The ultrastructural features of five pleomorphic rhabdomyosarcomas, five high-grade malignant fibrous histiocytomas, and five pleomorphic liposarcomas were studied. Electron microscopy was found to be consistently useful in distinguishing between these tumors. The rhabdomyosarcomas showed thick and thin filaments in complexes and consistently contained glycogen. The malignant fibrous histiocytomas had numerous lysosomes, often in cells with ruffled borders, and contained cells showing "myofibroblastic" differentiation. The liposarcomas showed abundant and coalescing lipid droplets, sparse stroma with condensation of amorphous granular materials surrounding plasma membranes, and prominent vascularity. Fourteen of the 15 tumors could be identified on the basis of ultrastructure; thus, electron microscopic examination is an important diagnostic tool for pleomorphic tumors.

Malignant soft tissue tumors (malignant fibrous histiocytoma, pleomorphic liposarcoma, and pleomorphic rhabdomyosarcoma): an electron microscopic study.

A comparative ultrastructural analysis of malignant soft tissue tumors (malignant fibrous histiocytoma, pleomorphic liposarcoma, and pleomorphic rhabdomyosarcoma) revealed similar ultrastructural features in this group of tumors. However, by electron microscopy these tumors can be differentiated on the basis of cytoplasmic and extracytoplasmic features (myosin filaments, lipid droplets, and perinuclear intermediate filaments, for example). This is even true of less well differentiated tumors and tumor cells. These findings support and amplify the concept of a common histogenesis for tumors of mesenchymal origin. Paradoxical features observed by light microscopy warrant further study by electron microscopy if the correct diagnosis is to be made in atypical cases, such as apparent malignant fibrous histiocytoma with cross striations.

Lipomatous tumors: a correlative cytologic and histologic study of 27 tumors examined by fine needle aspiration cytology.

A correlative cytologic and histologic study of 12 benign lipomatous tumors and 15 liposarcomas (well-differentiated, myxoid, round cell, and pleomorphic) is presented. In two cases the fine needle aspiration material was embedded in Epon for light and electron microscopic examination. Good correlation was found between the histologic and cytologic findings in the fine needle aspiration material. Pitfalls in the cytologic diagnosis of regressively changed lipoma, intramuscular lipoma, angiolipoma, hibernoma, and lipoblastoma, which may lead to an erroneous diagnosis of liposarcoma, are illustrated. The cytologic appearances of the liposarcomas varied with histologic type, although in all of these tumors the main criterion was the presence of atypical multivacuolated lipoblasts with characteristically scalloped nuclei. Staining of the aspirated material with Alcian blue at varying pH levels for characterization of the glycosaminoglycan content may help in the distinction of myxoid liposarcomas from myxoid chondromatous tumors and chordomas. May-Grünewald-Giemsa staining is considered the most useful staining method, while fat staining is considered of limited or no value in the cytologic diagnosis of lipomatous tumors. Epon embedding of fine needle aspirates for light and electron microscopic examination seems to be a useful diagnostic technique.

Myxoid liposarcoma. An ultrastructural study of two cases.

Two cases in which myxoid liposarcomas were examined by use of light and electron microscopy are presented. The relationship of this tumor to the development of normal adipose tissue is discussed. Most of the ultrastructural features were identical to those of developing white adipose tissue. Features not typical of developing white adipose tissue, such as congeries of 60-Angstrom filaments and large masses of glycogen, are also illustrated and discussed.

Liposarcoma. An ultrastructural study of 15 cases.

Fifteen liposarcomas from 13 patients were examined by electron microscopy. These included nine primary tumors, four recurrent tumors after primary surgery or irradiation, and two metastatic lesions. Twelve of the liposarcomas were located in the thigh, and 11 were of the myxoid variety. All neoplasms were composed of cells having the ultrastructural characteristics of some stage of lipoblastic differentiation, i.e., lipid droplets, micropinocytotic vesicles, glycogen, external lamina, intermediate filaments, Golgi apparatuses, rough and smooth endoplasmic reticulum, and mitochondria. The nuclear-cytoplasmic ratio and nuclear pleomorphism were related inversely to the size and number of lipid droplets. Lipoblasts were frequently in close association with capillaries and pericytes, and in four cases lipid droplets were found in pericytes. Multivacuolated, mitochondria-rich lipoblasts, resembling brown fat cells, also were seen. Most tumors contained lipid-free, poorly differentiated mesenchymal cells that showed a continuum of morphologic differentiation to cells that closely resembled early lipoblasts that contained nonmembrane-bound lipid vacuoles. Fibrolipoblasts, cells containing lipid droplets and abundant rough endoplasmic reticulum, were observed only in well-differentiated liposarcomas. Some soft tissue sarcomas contain vacuolated cells that simulate lipoblasts by light microscopy but prove to be reactive or malignant fibroblasts, histiocytes, or smooth muscle cells ultrastructurally. Therefore, use of electron microscopy may be necessary to establish the line of differentiation in these neoplasms.

A sarcoma of thymic stroma with features of liposarcoma.

A case of recurrent sarcoma arising from the stroma of the thymus and having the microscopic features of well-differentiated and pleomorphic liposarcoma is presented. No previous reference was found in the literature to this tumor type, which could be viewed as the malignant counterpart of thymolipoma.

Liposarcoma of the thyroid gland. Fine-needle aspiration cytology, immunohistology, and ultrastructure.

A 56-year-old woman presented with a rapidly growing tumoral mass of the thyroid. In fine-needle aspirates, neoplastic cells were interpreted as undifferentiated (anaplastic) carcinoma. In contrast, histologic examination of tissue samples revealed a tumor with features suggestive of myxoid liposarcoma. The non-epithelial nature was confirmed by immunohistochemical and electron microscopic evaluation. Immunostains for vimentin and S-100 protein were positive, whereas no reactivity was obtained for epithelial markers. Ultrastructurally, the tumor consisted of poorly differentiated mesenchymal cells and lipoblastic elements in various stages of differentiation. Review of the literature reveals only one previous report of thyroid liposarcoma, the diagnosis of which was based on conventional light microscopic studies.

Image cytometry analysis of Feulgen-stained nuclei in 72 lipomatous lesions including atypical lipomas and well-differentiated liposarcomas.

Well-differentiated lipomatous tumors constitute a histopathologic category whose nomenclature has been controversial, particularly with respect to the distinction between atypical lipomas of the extremities and well-differentiated liposarcomas of the retroperitoneum. To determine whether there were differences in image analytic parameters between these neoplasms, 72 lesions including 21 typical lipomas, 7 atypical lipomas, 16 retroperitoneal and 5 nonretroperitoneal well-differentiated, 9 dedifferentiated, and 14 pleomorphic liposarcomas were submitted to the computer-assisted microscopic analysis of Feulgen-stained nuclei. This methodology enabled four groups of variables to be calculated. These included: (1) quantitative chromatin pattern description (14 variables); (2) the measurement of proliferative activity (1 variable); (3) nuclear DNA content (DNA ploidy level, 5 variables); and (4) the measurement of cell density and topographical cell nuclei organization (2 variables). The results strongly suggest that atypical lipomas, whether superficial or deep, and well-differentiated liposarcomas, whether retroperitoneal or not, belong to the same category in terms of the variables analyzed.

Chromosome abnormalities in liposarcomas.

We performed a cytogenetic study of short-term cultures from fresh surgical specimens obtained from four patients with liposarcoma. Myxoid liposarcomas (cases 1-3) were associated with a specific translocation between chromosomes 12 and 16. Trisomy 8, a nonrandom secondary aberration in myxoid liposarcoma, was observed in the third case as the only additional change. Round cell liposarcoma (case 4) showed complex chromosomal aberrations affecting chromosomes 1, 2, 5, 6, 7, 13, 14, 17, 19, and 22. Neither band 12q13 nor 16p11 was visibly rearranged. Three subgroups of liposarcomas are proposed. The first group is characterized by t(12;16)(q13;p11), the second group by ring chromosomes, telomeric associations, and giant markers, and the last by complex numerical and structural aberrations.

Cytogenetic and fluorescence in situ hybridization investigation of ring chromosomes characterizing a specific pathologic subgroup of adipose tissue tumors.

Cytogenetic analysis of 184 adipose tissue tumors, 175 lipomas, and nine liposarcomas (LPS) showed the presence of a ring chromosome and/or a long marker chromosome in 10 cases with common histologic features such as atypical stromal cells with or without lipoblasts. In five of the cases, this appeared to be the sole cytogenetic abnormality. Fluorescence in situ hybridization (FISH) analysis with a microclone library specific for chromosome region 12q13-q15 showed extensive staining of the ring and long marker chromosomes, indicating that genetic sequences of this particular region of chromosome 12 are present in these marker chromosomes, most likely in an amplified form.

Morphologic-cytogenetic analysis of dedifferentiated liposarcomas with an extensive misleading leiomyosarcomatous component.

This report describes two cases of recurrent retroperitoneal dedifferentiated liposarcoma characterized by an extensive leiomyomatous component that prevented the correct diagnosis before the last recurrence. Strong immunoreactivity with smooth muscle and desmin antibodies and ultrastructural features consistent with leiomyosarcoma were observed in the spindle-cell and/or myxoid-like components in all four recurrences in case 1, and in the spindle-cell component of the primary tumor and the first recurrence in case 2. In case 1, the correct diagnosis was suggested by the cytogenetic evidence of ring markers, a hallmark of well-differentiated/dedifferentiated liposarcoma. In case 2, tumor type was yielded mainly by the morphology of the second recurrence, which consisted entirely of a well-differentiated liposarcoma, a sclerosing inflammatory variant, as confirmed by the karyotype. Reevaluation of the first two surgical specimens of each case revealed small areas consistent with well-differentiated liposarcoma that had been previously overlooked. Despite the smooth-muscle antigen profile, both cases retained an mdm2+/p53+/cdk4+ immunophenotype consistent with the genotype.

Recurrent dedifferentiated liposarcoma of the spermatic cord simulating malignant fibrous histiocytoma: an immunohistochemical and ultrastructural study.

A case of recurrent dedifferentiated liposarcoma simulating malignant fibrous histiocytoma, with complete absence of lipoblastic differentiation, is described. The tumour cells showed strongly positive immunostaining for alpha-1-antichymotrypsin. Electron microscopy revealed a mixture of fibroblasts and histiocytes. Our findings suggest that the dedifferentiated component reflects an altered differentiation pathway of the primitive mesenchymal cells in the original liposarcoma.

The contributions of electron microscopy in the diagnosis and histogenesis of controversial neoplasms.

In this article, several areas in the pathology of tumors are discussed in which electron microscopy has contributed valuable diagnostic information but, at the same time, has not resolved all the questions regarding histogenesis, differentiation, and cell type.

Mesenteric pleomorphic liposarcoma in an adolescent.

We report a case of pleomorphic liposarcoma arising in the root of the mesentery of an adolescent girl. Pleomorphic liposarcoma is an extremely rare tumor in the pediatric age group, and few well-documented cases are found in the literature. To the best of our knowledge, none have been described in the abdomen. The histologic and ultra-structural features of this tumor are described, and the literature concerning pediatric pleomorphic liposarcoma is reviewed.