Path. Res. Pract. 188,981-988 (1992)

Intra-Abdominal Desmoplastic Small-cell Tumours with Divergent Differentiation Report of Two Cases and Review of the Literature I. Nikolaou, C. Barbatis, V, Laopodis 1, S. Bekir2 and C. D. M. Fletcher2 Department of Histopathology and the lFirst DfJpartment of Surgery, Hellenic Red Cross Hospital, Athens, Greece; 2Soft Tissue Tumour Unit, Department of Histopathology, St Thomas's Hospital (U.M.D.S.), London, u.K.

SUMMARY Two intraabdominal desmoplastic small cell tumours presenting in young adult males and involving the entire peritoneum, with no evident single primary site, have been studied. The histological pattern was suggestille of a metastatic small cell epithelial neoplasm, but immunohistochemical study revealed strong reactillity for cytokeratins, llimentin and desmin indicating synchronous epithelial and myogenous differentiation. In addition epithelial membrane antigen and neuron specific enolase were also positive. Electron microscopy showed fairly undifferentiated tumour cells with striking desmosome-like junctions, containing prominent paranuclear whorls of intermediate filaments, and a typical myofibroblastic stroma around neoplastic islands. Although the histogenesis of these recently described and rare tumours still remains uncertain, it seems that they constitute a reproducible entity which requires differential diagnosis from other small cell tumours of childhood and young adulthood.

Introduction

Intraabdominal desmoplastic small cell tumour is a recently described, rare, malignant neoplasm of childhood and young adulthood 8, 11,25,31. The term used initially by Gerald and Rosai, when first describing this entityR was "Desmoplastic Small Cell Tumour with Divergent Differentiation", based on the primitive nature of the neoplastic cells and their diverse phenotypic differentiation. Their cases co-expressed cytokeratins (CK), vimentin (VIM) and desmin (DES), with the additional finding of neuron specific enolase (NSE) and S-100 protein positivity. The behaviour of these neoplasms was aggressive and their response to chemotherapy and radiation very poor. This original series has very" recently been published in expanded and more detailed form 9 . A second report followed from Ordonez et a12 5 , who reported one case with the same clinical, histological, © 1992 by Gustav Fischer Verlag, Stuttgart

immunohistochemical and ultrastructural characteristics under the term "Malignant Small Cell Epithelial Tumour of Peritoneum", suggesting that the tumour may arise from mesothelial or submesothelial cells. Their case also had a poor response to chemotherapy with a fatal outcome within !\vo years. Recently Gonzalez-Crussi et all! added three more examples under the descriptive term of "Intraabdominal Desmoplastic Small Cell Tumour with Divergent Differentiation". Their cases had the same reported immunophenotype with the additional expression of synaptophysin (SYN), while NSE was detected in only one case .and S-100 protein was negative in all cases. On electron microscopy, desmosome-like junctions, paranuclear accumulation of intermediate filaments and scattered electron dense inclusions were identified. One of these cases also responded poorly to chemotherapy and proved fatal within a year. The other two patients had a better response to chemotherapy and radiotherapy, one of them 0344·0338/92/0188-0981 $3.50/0

982 . I. Nikolaou et al.

dying six years after the initial operation while the other remained alive and tumour-free four years after disease onset. Very recently, Variend et al 31 reported two further cases under the heading "Intra-abdominal Neuroectodermal Tumour of Childhood with Divergent Differentiation", based on the identification of Homer-Wright rosettes, immunohistochemical expression of NSE and the ultrastructural identification of electron-dense granules. The tumour in one case seemingly decreased in size without treatment and remained stable for three and a half years, following which the patient deteriorated and finally died 18 months later with extensive intra-abdominal tumour. In the other case, chemotherapy led to considerable shrinkage of the neoplasm but the patient is still under follow-up with residual tumour and hepatic metastases. In the present paper we present two additional cases of intraabdominal desmoplastic small cell tumour with divergent differentiation, which exhibited an epithelial and myogenous immunohistochemical profile and similar ultrastructural characteristics to those previously described. In describing our difficulties in differential diagnosis, we discuss the potential multidirectional differentiation of these tumours in comparison with previously reported cases, in order to draw further attention to these distinctive tumours. Case Histories Case 1. A 29-year-old male presented with progressive weakness, loss of weight and severe left hip pain. Physical examination revealed palpable abdominal masses with inguinal and axillary lymphadenopathy. CT scan revealed intraabdominal and retroperitoneal masses, measuring approximately 3 to 8 cm, and multiple deposits in the liver, consistent with metastatic disease. Bone scan showed osteolytic lesions in the pelvis, adjacent to the left hip joint. Laparotomy was performed and numerous smooth, firm

serosal nodules, affecting the peritoneum, mesentery and retroperitoneum were seen; multiple metastases were noted in the liver. At frozen section a diagnosis of a high grade small cell malignant neoplasm, with features suggestive of metastatic carcinoma, (of unknown primary site), ,vas made. Subsequent extensive clinical and radiological investigation failed to identify any primary site, other than the intraabdominal and retroperitoneal tumours. The p~ltient received combination chemotherapy. He rapidly improved and his condition was stable for 14 months, but he was recently readmitted to hospital with ascites and cachexia. Seventeen months after his first admission, he remains alive with persistent tumour. Case 2. A 28-year-old male presented with an acute history of right-sided abdominal pain and vomiting. A clinical diagnosis of acute appendicitis was made, but at laparotomy the omentum, mesentery and entire peritoneal surface were studded by numerous smooth, hard nodules measuring up to 4 cm. A larger mass (8 em) was attached to the dome of the urinary bladder and extended to envelop both ureters. There was no obvious single primary site identified during laparotomy. He was treated with chemotherapy at another hospital. His most recent CT scan, 7 months after disease onset, revealed marked reduction in the tumour's size. He is still ,{live 10 months after diagnosis without apparent metastases.

Material and Methods Formalin-fixed and paraffin-embedded tissue was used for light and electron microscopy and for immunohistochemistry. Sections were stained with haematoxylin and eosin, periodic acid-Schiff (PAS), diastase/PAS and by the 1'1'1asson's trichrome technique. As preliminary immunohistochemical results revealed coexpression of CK, VIM, and DES, a wide panel of antibodies was selected for further investigation, as listed in Table 1.

Table 1. Panel of antibodies used Antibody

Type Source

Dilution

Keratin, Cam 5.2 Keratin MNF 116+LP34 Keratin 54+64KD Keratin 8+18+19 (52+45+40 KD) Epithelial Membrane Antigen (EMA) Vimentin (Vi) Desmin II (DII) Desmin 33 (D33) Alpha-Smooth Muscle Actin (SMA) Myoglobin (mg) Neurofilament 2Fll (NF) Glial Fibrillary Acidic Protein (GFAP) Neuron Specific Enolase (NSE) S-100 protein Protein Gene product 9.5 (PGP 9.5) Chromogranin (CHR) Synaptophysin (syn) Laminin (L) Collagen IV

M 1\1

l: 100 1: 20 1:400 1: 50 1: lOO 1: 20 I: 10 1: 50 1:800 1: 300 1: 20 1: 20 neat l: 200 l:800 1: 10 I: 10 1: 100 1: 500

P

1\1 1\1 1\1 1\1 1\1 M

P M M P P M M M P P

Becton Dickinson D. J\1ason, John Radcliffe Hospital, Oxford Dakopatts Sera-lab Sera-lab Dakop,~,,:,

Eurodiagnostics Dakopatts Sigma Chemical Co Dakopatrs D. Mason, John Radcliffe Hospital, Oxford D. Mason, John Radcliffe Hospital, Oxford Immunotech Dakoparrs Ultra -clone Euro-diagnostics Euro-diagnostics Euro-diagnostics Southern Biotechnology Ass. Inc.

Desmoplastic Small Cell Tumour· 983 The immunohistochemical methods used were peroxidase anti-peroxidase (PAP)28 for the polyclonal antibodies and the avidin-biotin-peroxidase (ABC) technique!7 for the monoclonals, while type IV collagen was detected by the Extravidin Biotin Goat staining kit (BioMakor). Limited trypsin digestion was performed for 10 minutes for polyclonal CK and for EM A, DB and S-100 protein antibodies. Slides for collagen type IV and laminin staining were digested with 0.4 % pepsin for 30 minutes. Endogenous peroxidase activity was blocked with 3 % hydrogen peroxide in absolute methanol for 10 minutes. Appropriate positive controls for each antibody were included; for negative controls we used the same tissue sections, incubated in normal swine serum instead of the primary antibody. For ultrastructural analysis, small fragments were retrieved from the paraffin blocks in each case. These were deparaffinised, rehydrated in graded alcohols, post-fixed in 1 % osmium tetroxide and were processed into araldite. Ultrathin sections were examined in a Philips 201 transmission electron microscope at 60KV.

Results

Macroscopic Findings As the disease was so extensive and unresectable in both cases, only a few omental and peritoneal tumour nodules (measuring 1.5 to 2.5 cm) were biopsied and sent for

Fig. 1. Case 1. Typical morphology of IDSCT, showing discrete islands of small, undifferentiated cells in a prominent spindlecelled desmoplastic stroma. H&E x 57.

histological examination. All nodules were smooth, hard and solid with a grey-white cut surface.

Histological Findings Case 1: The tumour consisted of variably sized, discrete islands of basophilic cells, a few of \,vhich exhibited central loss of cohesion and necrosis. These were embedded in an abundant cellular desmoplastic stroma (Fig. 1). Neoplastic cells were small to medium sized, and round, with distinct cytoplasmic borders (Fig. 2), quite often vacuolated, with occasional signet ring forms. Cytoplasm was generally scanty. Nuclei were round or oval with a vesicular chromatin pattern and one or more nucleoli. A considerable number of nuclei were pyknotic due to degeneration. Mitoses were abundant. The desmoplastic stroma consisted of bland, fascicular fibroblastic or myofibroblastic cells set in a collagenous matrix. Case 2: The tumour was arranged in coalescing irregular, cellular islands, showing focal central necrosis, separated by a limited fibrovascular desmoplastic stroma. Tumour islands and isolated neoplastic cell groups seemed to be surrounded, at least partially, by a layer of hyaline material (Fig. 3). Neoplastic cells were fairly undifferentiated and small with scanty basophilic, ill-defined cytoplasm and they exhibited progressive spindling with focal

Fig. 2. Case 1. The neoplastic small cells are variably round to spindle-shaped and often show pyknosis. H&E x 225.

984 . 1. Nikolaou et al.

Fig. 3. Case 2. In this "tumour, desmoplastic stroma was less ptominent but condensed hyaline material (arrows) was evident around some islands of tumour cells. H&E x 90.

Fig. 4. Case 1. Note the striking pan-keratin positivity with a mainly perinuclear distribution. ABC method x 225.

streaming and whorling. Nuclei were uniform and oval, with fine chromatin and with one or more nucleoli. Mitoses were again abundant. In neither case were glandular structures or rosettes identified although, in Case 1, very occasional spaces suggestive of incipient glandular or ductular differentiation were identified.

Immunohistochemistry Both cases showed a similar immunophenotype, with regard to the basophilic tumour cells. Low molecular weight CKs were widely expressed (80-95 % of tumour cells), either diffusely throughout the cytoplasm or in the perinuclear area (Fig. 4) while high molecular weight CKs were detected in only 20-25 % of neoplastic cells, staining mainly the perinuclear cytoplasm. EMA was identified on the cytoplasmic membrane of only a few small groups of neoplastic cells (2 %). Vimentin was strongly expressed throughout each tumour, either in the perinuclear cytoplasm of approximately 25 % of neoplastic cells or forming a distinct globoid paranuclear structure in 20 % of tumour cells. In contrast to vimentin, des min wasdetected in 90 % of neoplastic cells but with a similar perinuclear or paranuclear dot-like distribution (Fig. 5). NSE was diffusely positive in the cytoplasm of most neoplastic cells.

Fig. 5. Case 2. The majority of tumour cells are also desmin positive. ABC method x 225.

Desmoplastic Small Cell Tumour· 985

Fig. 6. Case 1. Tumour cells appear relatively undifferentiated but many contain prominent paranuclear filamentous aggregates. X 7,450.

Fig. 7. Case 2. Note the desmosome-like Junctions between tumour cells (above centre) and the filamentous aggregate (bottom right). X 30,375.

986 . 1. Nikolaou et al.

Cells in the desmoplastic stroma expressed only vimentin and smooth muscle actin (SMA). Both basement membrane components, laminin and type IV collagen, were detected only in case 2, partially surrounding the tumour islands or smaller isolated cell groups. All other markers used, including S-100, neurofilaments, synaptophysin, GFAP and PGP 9.5, were not reactive with the tumour cells.

some-like junctions (Fig. 7). No basal lamina was identified in either case but, in case 2, these cellular islands were separated from the adjacent desmoplastic stroma by a layer of dense flocculent material. Within desmoplastic areas, as expected, cells showed the typical features of myofibroblasts, with dilated rough endoplasmic reticulum and longitudinal bundles of filaments with dense bodies (Fig. 8). These cells were set in a loose collagenous stroma.

Electron Microscopy

Ultrastructural analysis was impaired to some extent by the use of formalin-fixed, paraffin-embedded tissue. However, the findings in each case were similar. The groups of small round tumour cells were fairly undifferentiated and contained sparse organelles, predominantly mitochondria. Dense-core granules were not identified. Nuclei were round to oval with irregular infoldings and prominent heterochromatin. Many of the cells contained prominent intermediate filaments, which were often aggregated in paranuclear whorls (Fig. 6). Some cells contained small amounts of glycogen and others showed striking desmo-

Discussion Both tumours affected young adult males, who presented with intraabdominal malignant disease involving the omentum, mesentery and the peritoneal surface of intraabdominal organs, while in one case there was also retroperitoneal, liver, lymph node and bone involvement. In both cases no specific single primary site could be identified. Both tumours were macroscopically and histologically compatible with those recently described under

.. • ~

•I

.

•

."

-. .

Fig. 8. Case 1. Cells in the desmoplastic stroma contain bundles of filaments with focal densities, in keeping with myofibroblasts. x 16,000.

Desmoplastic Small Cell Tumour . 987

the rubric "Intraabdominal Desmoplastic Small-Cell Tumour with Divergent Differentiation" (IDSCT) and which appears to be a distinctive and cohesive entity9. Co-expression of two different classes of intermediate filaments is not infrequent in human tissues and CKs are often involved in this phenomenon. Several papers have demonstrated this co-expression in a wide variety of normal resting and proliferating cells as well as in diverse human neopl asms 3,14,20-24. Co-expression of three intermediate filaments such as CK, VIM and DES is a rare phenomenon but has been described in normal mesothelial cells and mesotheliomas 30 , in fetal and adult smooth and striated muscle cells and neoplasms thereof2,4, 13, 18, in primitive neuroectodermal rumours of the central nervous system 12 , in extra-renal rhabdoid tumours 7 and in the recently described entity of intraabdominal desmoplastic small-cell tumour 9, 11,25,31. Although it is now realised that a broad degree of homology exists between the different classes of intermediate filaments and between certain intermediate filaments and other nuclear associated proteins, it seems, at least in some cases, documented by a wider panel of antibodies, electron microscopy or gel electrophoresis, that this co-expression is reaPO,15,34. In our cases, the use of a wide panel of antibodies has produced results strongly suggestive of co-expression of three classes of intermediate filaments. Paranuclear accumulation of filamentous material, identified ultrastrucrurally and corresponding in location to the dot-like positivity of VIM and DES, has been described in the previously reported cases of IDSCT. Similar ultrastrucrural paranuclear whorls of different classes of intermediate filaments have been described in other human neoplasms of varying organs 1,5,26,33, and, in fact, are a distinctive feature of extra renal rhabdoid rumours, which often show a complex immunophenotype7 • Our main differential diagnosis included: metastatic carcinoma, solid variant alveolar rhabdomyosarcoma, extra skeletal Ewing's sarcoma, peripheral neuroepitheliorna, neuroendocrine tumour and mesothelioma. Expression of NSE in both our cases provides insufficient evidence, in our opinion, for neuroendocrine or neuroectodermal differentiation as neurosecretory granules were not identified at electron microscopy and other, possibly more specific, neuroectodermal markers, such as S-100, neurofilaments and synaptophysin, were negative. The presence of NSE, a glycolytic enzyme, in various hyperplastic or neoplastic cells is not considered specific and may well be related to increased metabolic demand with augmentation of the rate of glycolysis16,32. The possibility of metastatic carcinoma was excluded by the lack of any other specific primary site and by the expression of desmin. Solid variant alveolar rhabdomyosarcoma was a likely histological and immunohistochemical diagnosis but was excluded by the lack of ultrastructural evidence or myoglobin expression, combined with the presence of EMA positivity and the distinctive clinical setting. Extraskeletal Ewing's sarcoma was also seriously considered but the cytoplasm contained veryJimited glycogen, while desmin expression and paranuclear whorls of intermediate filaments are not features of Ewing's sarcoma.

As both malignant neoplasms affected primarily the abdominal peritoneal surface and since co-expression of cytokeratin, vimentin and desmin along with paranuclear whorls of intermediate filaments have been reported in mesothelioma 3o , our cases had to be distinguished from a mesothelial rumour. Both patients were young, they had not been exposed to asbestos and the histological pattern did not resemble the classically recognised types of mesothelioma 19. It has been proposed by some authors 9 ,25 that these small cell tumours of peritoneum in young individuals may perhaps arise from mesothelial or submesothelial cells. Certainly the diffuse involvement of the peritoneum in this characteristic fashion would support that suggestion, as would the proven capacity of mesothelial cells to adopt a myogenic phenotype6 • However, ultrastructural evidence of true mesothelial differentiation is as yet lacking. Our cases differed from some of those previously reported, as we did not identify electron dense granules ultrastructurally. Only in one previous case31 did these really resemble typical neurosecretory granules. Hence the term "Intraabdominal Neuroectodermal Tumour of Childhood with Divergent Differentiation"31 does not seem fully justified nor has it been supported by more specific immunohistochemical markers of neuroectodermal differentiation. Both our cases have a similar immunohistochemical and ultrastructural profile to Swanson et aI's "polyphenotypic small cell tumours of childhood"29 and to some cases in Moll et aI's study of Ewing's sarcomas23, which stressed the similarities of primitive bone and soft tissue lesions with a variable phenotypic profile and suggested multidirectional differentiation with possible redesignation as "blastomas". These latter also responded fairly well to combined chemotherapy. At the moment the rather descriptive term of "Intraabdominal Desmoplastic SmallCell Tumour with Divergent Differentiation" seems to be the most appropriate for the distinctive neoplasms described herein. Further study of this entity and other related small cell tumours of young individuals may help to clarify their complex phenotype and cytogenetic analysis, in particular, may provide a basis for a more reproducible classification if the presence of translocation t(11 ;22)(q24;q13), so typical of other peripheral primitive neuroectodermal tumours 7 , could be identified. References 1 Battifora H, Silva EG (1986) The use of antikeratin antibodies in the immunohistochemical distinction between neuroendocrine (Merkel cell) carcinoma of the skin, lymphoma and oat cell carcinoma. Cancer 58: 1040-1046 2 Brown DC, Theaker ]M, Banks PM, Garter KC, Mason DY (1987) Cytokeratin expression in smooth muscle and smooth muscle tumours. Histopathology 11: 477-486 3 Churg A (1985) Immunohistochemical staining for vimentin and keratin in malignant mesothelioma. Am ] Surg Pathol 9: 360-365 4 Coindre ]M, De Mascarel A, Trojani M, De Mascarel I, Pages A (1988) Immunohistochemical study of rhabdomyosarcoma.

988 . 1. Nikolaou et al. Unexpected staining with S-l 00 protein and cytokeratin. J Pathol 155: 127-132 5 Dardick I, Al-Jabi M, McCaughey WT, Srigley JR, Nostrand AWP, Ritchie AC (1984) Ultrastructure of poorly differentiated diffuse epithelial mesotheliomas. Ultrastruct Pathol 7: 151-168 6 Donna A, Betta PG, Bianchi V, Ribotta M, Bellingeri D, Robutti F, Marchesini A (1991) A new insight into the histogenesis of 'mesodermomas' - malignant mesotheliomas. Histopathology 19: 239-243 7 Fletcher CDM, McKee PH (1990) Pathobiology of Soft Tissue Tumours. Churchill Livingstone, Edinburgh S Gerald WL, Rosai J (1989) Desmoplastic small cell tumour with divergent differentiation. Pediatr Pathol 9: 177-183 9 Gerald WL, Miller HK, Battifora H, Miettinen M, Silva EG, Rosai J (1991) Intra-abdominal desmoplastic small round cell tumour. Report of 19 cases of a distinctive type of high grade polyphenotypic malignancy affecting young individuals. Am J Surg Pathol15: 499-513 10 Goldman AE, Maul G, Stener PM, Yong HY, Goldman RD (1986) Keratin-like proteins that conjoin with intermediate filaments of BHK-21 cells are nuclear lamins. Proc Natl Acad Sci USA 83: 3839-3843 11 Gonzalez-Crussi F, Crawford SE, Sun JC (1990) Intraabdominal desmoplastic small-cell tumours with divergent differentiation. Observations on three cases of childhood. Am J Surg Pathol 14 (7): 633-642 12 Gould V, Rocke L, Jansson D (1990) Primitive neuroectodermal tumours of the central nervous system express neuroendocrine markers and may express all classes of intermediate filaments. Human Pathol 21 (3): 245-252 Ll Gown AM, Boyd HC, Chang Y, Ferguson M, Reichler BS, Tippeus D (1988) Smooth muscle cells co-express cytokeratins of "simple" epithelium. Immunocytochemical and biochemical studies in vitro and in vivo. Am J Pathol 132 (2): 233-232 14 Gray M, Rosenberg A, Bhan A, Dickersin G (1990) Cytokeratin expression in epithelioid vascular neoplasms. Human Pathol 21: 212-217 15 Gusterson BA (1987) Is keratin present in smooth muscle? Histopathology 11: 549-552 16 Haimoto H, Takahashi Y, Koshikawa T, Naguro H, Kato K (1985) Immunohistochemical localization of gamma enolase in normal tissues other than nervous and neuroendocrine tissues. Lab Invest 52: 257-263 ]7 Hsu SM, Raine L, Fanger H (1981) Use of avidin-biotin peroxidase complex (ABC) in immunoperoxidase techniques. A comparison between ABC and unlabelled antibody (PAP) procedures. J Histochem Cytochem 29: 577-580 18 Huitfeldt HS, Brandtzaeg P (1985) Various keratin antibodies produce immunohistochemical staining of human myocardium and myometrium. Histochem 83: 381-389

19 Jones JSP, Lund C, Planteydt HT, Butler EB (1985) Color Atlas of Mesothelioma. MTP Press, Boston Kluwer 21l McNutt MA, BolenJW, Gown AH, Hammar SP, Vogel AM (1985) Expression of intermediate filaments in human epithelial neoplasms. Ultrastruct Pathol 9: 31-43 21 Meis JM, Ordonez NG, Brumer JM (1986) Meningiomas: An immunohistochemical study of 50 cases. Arch Pathol Lab Med 110: 934-937 22 Miettinen M, Lehto V-P, Dahl D, Virtanen I (1985) Varying expression of cytokeratin and neurofilaments in neuroendocrine tumours of human gastrointestinal tract. Lab Invest 52: 429-436 23 Moll R, Lee I, Gould V, Berndt R, Roessner A, Franke WW (1987) Immunocytochemical analysis of Ewing's tumours: patterns of expression of intermediate filaments and desmosomal proteins indicate cell type heterogeneity and pluripotential differentiation. Am J Pathol127: 288-304 24 Ng HK, Lo STH (1989) Cytokeratin immuno-reactivity in gliomas. Histopathology 14: 359-356 25 Ordonez GN, Zirkin R, Bloom RE (1989) Malignant small-cell epithelial tumor of the peritoneum co-expressing mesenchymal type intermediate filaments. Am J Surg Pathol13: 413-421 26 Sheibani K, Battifora H (1985) Signet ring cell melanoma. A rare morphologic variant of malignant melanoma. Am J Surg Pathol 12: 28-34 27 Sotelo-Avila C, Gonzalez-Crussi F, de Mello D, Vogler C, Gooch WM, Gale G, Pena R (1986) Renal and extrarenal rhabdoid tumours in children: a clinicopathologic study of 14 patients. Semin Diagn Pathol3: 151-163 28 Sternberger L (1979) Immunohistochemistry, 2nd edition. John Wiley and Sons, New York 29 Swanson PE, Dehner LP, Wick MR (1988) Polyphenotypic small cell tumours of childhood (Abstract). Lab Invest 58: 9P 30 Van Muijem GNP, Ruiter DJ, Warmaar SO (1987) Coexpression of intermediate filament polypeptide in human fetal and adult tissues. Lab Invest 57: 359-369 31 Variend S, Gerrard M, Morris PD, Goepel JR (1991) Intraabdominal neuroectodermal tumour of childhood with divergent differentiation. Histopathology 18: 45-51 32 Vinores SA, BonnimJU, Rubinstein LJ, Marangos PJ (1984) Immunohistochemical demonstration of neuron-specific enolase in neoplasms of the central nervous system and other tissues. Arch Pathol Lab Med 108: 536-540 33 Warner TFCS, Seo IS (1980) Aggregates of cytofilaments as the cause of the appearance of hyaline tumor cells. Ultrastruct Patholl: 395-401 34 Zockroff PV, Goldman AE, Jones JCR, Steinhert RM, Goldman RD (1984) Isolation and characterisation of keratinlike proteins from cultured cells with fibroblastic morphology. J Cell Bioi 98: 1231-1237

Received October 14, 1991. Accepted January 14, 1992

Key words: Small cell tumour - Peritoneum sarcoma - Primitive neuroectodermal tumour - Mesothelium Dr. CDM Fletcher, Soft Tissue Tumour Unit, Department of Histopathology, St. Thomas Hospital, London SE1 7EH, UK