Ampullary Somatostatinoma

Path. Res. Pract. 183, 1-7 (1988)

Diagnostic Seminar

Malignant Fibrous Histiocytoma History, Histology, Histogenesis * P. Meister Stadt. Krankenhaus Miinchen-Harlaching, F.R.G.

SUMMARY

At the XVI. International Congress of the International Academy of Pathology (Vienna, 1986), a session was dedicated to the classification ofsoft tissue tumors. At this occasion a critical review of malignant fibrous histiocytoma (MFH) was presented. A) The history ofMFH revealed that this tumor had been known for many years under a variety of names. Moreover, MFH apparently had frequently been misinterpreted as other tumor types, as for instance rhabdomyosarcoma. Today, there is a discrepancy between the high incidence of MFH among soft tissue sarcomas and its underrepresentation in some widely used tumor classifications. B) The histological appearance may be fully developed and typical for MFH. However, it also may be merly compatible with MFH in less typical tumor areas. Regional differences in morphological appearance may be pronounced. Differential diagnosis can be helped by histochemical methods. C) Histochemical methods-among others- also help to shed light on the histogenesis. More recent findings point to MFH, as a tumor of fibroblasts rather than histiocytes with similarities to loose areolar connective tissue. Although MFH-like areas may occur focally within a variety ofdifferent tumors, there remains a large group ofsarcomas which do not display any signs of further differentiation even after careful work-up. In these cases the application of the term MFH, as it is understood today, appears to be justified.

History In the first printing of the Tumor Atlas Fascicle on Soft Tissue Tumors (2nd series, 1966/AFlP, chapter about "Malignant Histiocytic Tumors") the question was raised, "whether or not benign fibrous histiocytic tumors ever became malignant fibrous histiocytomas"sl. To the best of my knowledge, this is the first time the full term of "malignant fibrous histiocytoma" (MFH) can be found in print. Fifteen years later, in the first revision of this tumor fascicle, the following synonyms and related terms are listed * This publication is based on material presented at the WHO-Session on classification of soft tissue tumors at the XVI. International Congress of the International Academy of Pathology in Vienna, 1986. © 1988 by Gustav Fischer Verlag, Stuttgart

under the heading of malignant histiocytic tumors: "malignant fibrous histiocytoma"; "malignant fibrous xanthoma"; "malignant xanthofibroma"; "fibroxanthosarcoma"; "malignant giant cell tumor of soft parts,,29. Classical descriptions of MFH have been published by Stout and coworkers as "histiocytic tumors (fibrous xanthoma and histiocytoma) in children,,21- which by the way is not a patient group of predilection-, "malignant histiocytomas and fibrous xanthomas,,44 and "malignant fibrous xanthoma,,43 but not as MFH. Moreover, both "malignant xanthogranuloma", a term coined by Oberling in 1935 42 and "fibroxanthosarcoma" reported by N6then in 192041 , would be classified as MFH by contemporary usage of this term. The first edition of the Histological Typing of Soft Tissue Tumors, issued by the World Health Organization 0344-0338/88/0183-0001$3.50/0

2 . P. Meister (WHO) in 1969 10 , lists and describes tumOrS compatible In recent years, however, publications defining and reafwith MFH in the chapter dealing with tumors of disputed firmin~ MFH morphologically and biologically preOr uncertain histogenesis, as "malignant fibroxanthoma" vailed ,57. In these articles the histological features are "malignant histiocytoma" and "malignant giant cell well described, but the question of histogenesis is left open tumOr of soft parts" not making use of the term MFH. The for discussion. WHO volume of the typing of skin tumOrS published in 1974, does not include a chapter dealing with mesenchymal tumors of disputed or uncertain histogenesis and does Histology not mention the terms "fibroxanthosarcoma", "malignant histiocytoma". Among tumor-like xanthomatous lesions, Nowadays, the histological features of MFH are com"atypical fibroxanthoma" is described and depicted, mon knowledge to pathologists, especially in its typical which by some is considered to be a dermal MFW. MFH . form: a mixture of round and spindle cells, as well as also cannot be found in the Histological Typing of Bone multinucleated giant cells and optional xanthomatous Tumors by the WHO. - Finally, in the coded compendium cells 9, 29. Characteristic is a whorled or storiform pattern of classification of tumorS (WHO 1978), "malignant fibof spindle cells and collagen fibers, commonly found in roxanthoma" and "malignant histiocytoma" are assigned predominantly monomorphic fibroblastic tumors. This two different code numbers. In an addendum it is stated storiform pattern, however, is not ubiquitous 34 . MFH may "that malignant histiocytoma is coded to MFH,,51, being show marked local variations in the amount of intercelluconsidered a synonym. Obviously MFH, a term widely lar substances. Sclerosing and often hyalinized areas may used by pathologists not only for soft tissue tumors, is alternate with myxoid regions. The latter predominate in inadequately dealt with in various WHO-volumes on histhe myxoid variant of MFH, a tumOr with a supposedly tological typings of tumors. better prognosis59 • In spite of tumOr heterogeneity and The following reasons may be discussed as possible variable overlapping morphological features, a subclassifiexplanations for this: cation into four different variants has been suggested, 1. MFH is indeed a very rare tumor, which only recently because of morphological and clinical differences 9: a) has been recognized and previously had been overlooked; pleomorphic-storiform (classical MFH), b) myxoid59 , c) 2. MFH only recently has developed and did not exist inflammatory26, d) giant cell ("malignant giant cell tumOr before; of soft tissue")I, 12 and e) angiomatoid8. 3. MFH previously had been classified under other sarb), c), d) and e) usually show little collagen formation, c) comatous entities, and finally; disseminated leucocytes, plasma cells Or lymphocytes 4. MFH is not acceptable as tumor entity. without associated necrosis, d) numerous multinucleated giant cells, also without distinct atypia, as well as a typiAd 1.: MFH is not rare, but, on the contrary, is the cally prominent vascular pattern and peripheral inflamcommonest soft tissue sarComa in adults according to several studies 6, 7, 15, 20, 50, 58. In our revised diagnoses of matory rim, e) large blood spaces with debated existence totally 11·876 soft tissue tumors, 488 of which were of a proper lining, and occurrence in young patients with malignant, MFH was the commonest sarComa with 101 low incidence of metastasis. Other proposed subclassificacases, followed by liposarcoma with 76 cases37 . tions into a) fibroblastic, b) histiocytic and c) pleomorphic Ad 2.: this review of our material, in which the diagtype 15 correspond to experiences of daily practice. Hownosis of MFH originally has never been made, as well as ever, they frequently appear to be rather a focal expression of different patterns, all within the classical pleomorphic older case reports by Oberling (1935)42 and N6then (1920)41 also support the assumption that MFH did exist storiform type of MFH, and probably are of no biological before this term was coined and its features properly and prognostic significance. Based on cellular atypism, described. So, it must have been classified under different presence of undifferentiated (unclassifiable) cells and mitotic activity, a grading of MFH from G1-G4 can be names. Ad 3.: pleomorphic MFH, for example, could have been carried out (TNM/G!). Because of regional differences, hisdiagnosed as A) "pleomorphic rhabdomyosarcoma in tological examination of multiple tissue samples is manadults" because of brick red cytoplasm with questionable datory to ascertain that all different tumor portions showcross striations, chiefly in tumor giant cells, B) pleomoring variations in color and consistency are represented. phic liposarcoma, because of cytoplasmic vacuolization This is true not only for the evaluation of possible subtyand fat, C) grade 3-4 fibrosarcoma, because of collagen pes, but also for the diagnosis of MFH in general, as MFHproduction and cellular pleomorphism. - MFH with like features may also occur in other sarcomas, e.g. prominent myxoid changes supposedly were frequently liposarcomas, osteosarComas. Also, in the absence of a considered to be a) myxoid liposarcoma, b) myxoid rhabstoriform pattern, a mixture of spindly fibroblast-like, domyosarcoma, c) neurogenic sarComa Or neurofibroma, roundish histiocyte-like and atypical multinucleated d) myxoid fibrosarcoma (respectively "myxofibrosartumOr giant cells with pleomorphic appearance are typical coma")38. For the latter, as for fibrosarcoma grade 3-4, findings, which allow the diagnosis of MFH (Fig. 1). In the distinction from MFH is debatable. this context, less characteristic fibrous (Fig. 2) Or myxoid (Fig. 3) tumor areas, without pronounced pleomorphism AdA.: MFH is not a true tumor entity, but only a hodge podge of different tumors, as expressed in the title of one are also compatible with MFH, assuming that the hispaper concerning MFH of bone: "MFH-fact of fancy?"4. tological sections are representative.

Malignant Fibrous Histiocytoma . 3 .... Fig. 1. MFH with typical combination of elongated fibroblastlike cells, rounded histiocyte-like cells and atypical multinucleated giant cells. H & E, x 250.

Fig. 3. MFH (same tumor) myxoid area with only moderate pleomorphism, some whorling ("storiform pattern") and typical prominent vasculature. H & E, x 250.

.... Fig. 2. MFH (same tumor) Chiefly "fibroblastic" area with only moderate pleomorphism, rich in collagen and shoring fibrosarcoma-like fascicles. H & E, x 250.

4 . P. Meister

Histogenesis Accepting MFH as a tumor of fibroblast- and histiocytelike cells, the following concepts for histogenesis are feasible49 : A) MFH is a neoplasm purely of histiocytes, which may function as "facultative fibroblasts,,44; B) MFH is exclusively a tumor of fibroblasts, which may function as histiocytes, or finally C) MFH originates from undifferentiated mesenchymal cells, which may differentiate towards fibroblasts and histiocytes1, 11. In early studies based on tissue cultures, Ozello and Stout, the original describers, emphasized the histiocytic nature of MFH, a concept that was also reflected in the terminology ("malignant histiocytoma")44. Later, this concept was also thought to be supported by fine structural studies53 • Finally, a general agreement was reached that MFH was composed of fibroblastic and histiocyte-like cells, as well as undifferentiated or intermediary cells, xanthoma cells and giant cells1, 11, 17, 27, 29, 38a, 56. The presence of intermediate or undifferentiated cells was considered by some as evidence of a common stem cell origin, by others as evidence of the existence of a transitional stage in the transformation of fibroblasts to histiocytes, or vice versa. Myofibroblasts, emphasized in a

finestructural study of MFH as salient and common constituent of MFH can be thought of as functional variants of fibroblasts 3, 14. Recently, based on finestructural and immunohistochemical studies, the presence of "true histiocytes" in MFH was questioned. It also was argued that the neoplastic cells of MFH do not express the encymatic profile of the bone marrow derived monocyte/macrophage lineage 6o • In recent years, the histogenetic concert of MFH has shifted from histiocytes to fibroblasts 9, 1 , 60. Also, undifferentiated or intermediary cells were (in general) reported with and accepted in MFH 29 . However, there is no evidence of specific differentiations, besides collagen production and capability of phagocytosis, such as differentiation towards striated muscle cells etc. 39, 47, 48. The positive decoration of tumor cells with desmin could be explained solely by the presence of myofibroblasts in MFH. Moreover, since on critical analysis "pleomorphic rhabdomyosarcomas in adults" frequently lack proof of muscular differentiation39, the diagnosis of many of these tumors had to be changed from pleomorphic rhabdomyosarcoma to MFH. Evidently additional methods, such as tissue cultures, fine-structural and immunohistochemical analysis are needed to further elucidate the histogenesis of MFH. A

Fig. 4. MFH (as in Fig. 1) showing decoration with alpha-I-antichymotrypsin in fibroblast-like cells, histiocyte-like cells and multinucleated giant cells. x 2s50. PAP.

Fig. 5. Fetal loose connective tissue, showing decoration of some of the elongated fibroblast-like cells with alpha-1-antichymotrypsin. x 250. PAP.

Malignant Fibrous Histiocytoma . 5 recent cell-biological characterization of tumor cells suggested MFH to be a heterogeneous group of tumors, consisting either of undifferentiated primitive mesenchymal cells or of immature fibroblasts 48 . The few cases included in this study revealed no signs of further differentiation. Our experience concerning the histogenesis of MFH is based chiefly on the immunohistochemical findings, with results similar to those reported by other investigators5, 23, 32, 35, 36, 40, 45, 49. In contrast to reactive histiocytes in inflammation, which as a rule were positive for lysozyme, 19 of our 35 cases of MFH lacked positive decoration with lysozyme. However, a majority of 26 of these 35 cases of MFH showed positive reaction with alpha-1-antichymotrypsin not only in a great number of histiocyte-like cells, but also in fibroblast-like tumor cells35 (Fig. 4). These findings again support the concept that MFH consists of a proliferation of cells, which are either fibroblast-like or histiocyte-like, as originally stated52 • This also could be seen as evidence against the presence of "true" histiocytes in MFH, as in inflammatory reaction 45 , 60. The WHOclassification of Tumors being designated as "histiogenetic tumor classification", MFH should not be compared to different types of cells, but rather to types of normal tissue. According to some standard histologic texts, loose connective tissue in fetuses and adults is chiefly composed of fibroblasts, followed in the second place by "histiocytes"2, 33. In a semiquantitative comparative study of loose connective tissue in fetuses and adults, we observed immunohistochemical similarities as to the positive reaction of fibroblast-like and histiocyte-like cells with lysozyme and especially alpha-1-antichymotrypsin (Fig. 5)25. These findings suggest that MFH could be considered to be the neoplastic counterpart of loose connective tissuerespectively "undifferentiated mesenchyme". Alpha-1-antichymotrypsin is not a specific marker for histiocytes or histiocytic tumors 36, 45. However, used discriminatingly, it is a useful tool in the differential diagnosis of MFH; e.g. in combination with desmin it serves to separate pleomorphic MFH from rhabdomyosarcoma and other tumor types. Conclusion Frequently the question is raised, whether MFH is only a diagnostic "waste basket" for sarcomas that are difficult to classify? The situation reminds one of the "natural history" of hemangiopericytoma: immediately after its description it was only rarely diagnosed, later it was very much in vogue and overdiagnosed and today is still accepted as tumor entity, despite the fact that a regional hemangiopericytoma pattern may also be present in other types of tumors56 . Also with MFH the material examined has to be representative of the tumor as a whole. If there is no other differentiation recognizable and the features of MFH are exclusive, the diagnosis of MFH should be made. There may be a wide range of features and the distribution of fibroblast-like, histiocyte-like, giant- or xanthoma cells may show considerable regional variation within the same tumor. These variations have to be considered when

rendering the diagnosis of MFH. Since, so far, the biological significance of the above mentioned histological features is not known, a subclassification into four types, as previously proposed9, is favored, that at least seems to show some clinico-pathological correlations: A) classical pleomorphic-storiform MFH - the largest group with the largest range of variations, B) myxoid type, C) giant cell type and D) angiomatoid type-whereby especially the latter is marked by a lesser degree of malignancy. Histogenetically, a great proportion of MFH can be considered to be poorly differentiated fibroblastic sarcomas, showing some resemblance to loose areolar connective tissue in fetus and adult. Especially in analogy to fetal connective tissue, consideration must be given to the possibility that some cases of MFH are sarcomas of primitive mesenchymal cells, which retained a potential for multi-differentation along different lines. This concept also may explain why a) otherwise better differentiated sarcomas such as liposarcomas and osteosarcomas may show foci of MFH and why b) MFH-like tumors frequently occur in spontaneously or therapeutically induced "dedifferentiations" of originally higher differentiated sarcomas (for instance rhabdomyosarcoma or chondrosarcoma)9, 57. The role of MFH as the primitive sarcoma is also underlined by observations of MFH:Eattern in therapeutically induced rumors in men 13, 19, 30, Ii and also with exerimentally produced tumors in animals 24 . Whereas classical fibrosarcoma, rich in collagen, can be considered to be the neoplastic counterpart of dense, tendon-like connective tissue, MFH can be placed histogenetically between the primitive undifferentiated mesenchymal tissue and tendon-like connective tissue, often revealing similarities to fetal or adult loose areolar connective tissue. The latter, like MFH also consists of a variety of cell types, dominated by collagen producing fibroblast-like-cells- and "histiocytes", or histiocyte-like cells with capability to phagocytosis. In memoriam: the late Prof. Dr. Walter Biingeler. Supported by W. Sander-Foundation Publication of color micrographs was kindly supported by DAKO/Hamburg, F.R.G. References I Alguacil-Garcia A, Dnni K, Goellner R (1977) Malignant giant cell tumor of soft parts. Cancer 40: 244-253 2 Bucher (1980/81) Cytologie, Histologie und mikroskopische Anatomie des Menschen. H Huber, Bern, Stuttgart, Wien 3 Churg AM, Kahn LB (1977) Myofibroblasts and related cells in malignant fibrous and fibrohistiocytic tumors. Hum Pathol 8:

°

205-218

4 Dahlin DC, Dnni KK, Matsumo T (1977) Malignant (fibrous) histiocytoma of bone - fact or fancy? Cancer 39:

1508-1516

5 Du Boulay (1982) Demonstration of alpha-I-antitrypsin and alpha-l-antichymotrypsin in fibrous histiocytomas using the immunoperoxidase technique. Am J Surg Pathol 6: 559-564 6 Ekfors TO, Rantakokko V (1978) An analysis of 38 malignant fibrous histiocytomas in the extremities. Acta Pathol Microbiol Scand 86: 25-35

6 . P. Meister 7 Enjoji M, Hashimoto H, Iwasaki H (1980) Malignant fibrous histiocytoma. Acta Pathol jpn 30: 727-741 8 Enzinger FM (1979) Angiomatoid malignant fibrous histiocytoma. A distinct fibrohistiocytic tumor of childrend and young adults simulating a vascular neoplasm. Cancer 44: 2147-2157 9 Enzinger FM (1986) Malignant fibrous histiocytoma 20 years after Stout. Am j Surg Pathol 10 (sup!. 1) 43-53 10 Enzinger FM, Lattes R, TorIoni R (1969) Histologic typing of soft tissue tumours International Histological Classification of Tumours No.3. Geneva: World Health Organization 11 Fu YS, Gabbiani G, Kaye GI, Lattes R (1975) Malignant soft tissue tumors of probable histiocytic origin (malignant fibrous histiocytoma): General considerations and electron microscopic and tissue culture studies. Cancer 35: 176-198 12 Guccion jG, Enzinger FM (1972) Malignant giant cell tumor of soft parts. Cancer 29: 1518-1529 13 Hardy TV, An T, Brown PW, Tertz jj (1978) Postirradiation sarcoma (malignant fibrous histiocytoma) of axilla. Cancer 42: 118-124 14 Harris M (1980) The ultrastructure of benign and malignant fibrous histiocytomas. Histopathology 4: 29-44 15 Haydu S (1979) Pathology of soft tissue tumors. Lea & Febiger, Philadelphia 16 Hoffmann MA, Dickersin GR (1983) Malignant fibrous histiocytoma. An ultrastructural study of eleven cases. Hum Pathol14: 913-922 17 Inada 0, Yumoto T, Furuse K (1976) Ultrastructural features of malignant fibrous histiocytoma. Acta Pathol jpn 26: 491 18 Inoue A, Aozasa K, Tsujimoto M, Tarnai M, Chatani F, Ueno H (1984) Immunohistochemical study of malignant fibrous histiocytoma. Acta Pathol jpn 34: 759-765 19 Inoshita T, Youngberg GA (1984) Malignant fibrous histiocytoma arising in previous surgical sites. Report of two cases. Cancer 53: 176-183 20 Iwasaki H, Kikuchi M, Takii M, Enjoji M (1982) Benign and malignant fibrous histiocytomas of the soft tissues. Functional charakterization of the cultured cells. Cancer 50: 520-530 21 Kauffmann SL, Stout AP (1961) Histiocytic tumors (fibrous xanthoma and histiocytoma) in children. Cancer 14: 469-482 22 Kempson RL, Kyriakos M (1972) Fibroxanthosarcoma of the soft tissues: A type of malignant fibrous histiocytoma. Cancer 29: 961-976 23 Kindblom LG, jacobsen GK, jacobsen M (1982) Immunhistochemical investigations of tumors of supposed fibroblastic-histiocytic origin. Hum Pathol 13: 834-840 24 Konishi Y, Maruyana H, Mii Y, Mijauchi Y, Yokose Y, Masuhara K (1982) Malignant fibrous histiocytoma induced by 4-(hydroxy-amino) quinoline I-oxide in rats. j Natl Cancer Inst 68: 859-865 25 Kretzschmar H (1984) Quantitative immunhistochemische Untersuchungen zur Histogenese der malignen fibr6sen Histiozytome. Aus dem Pathologischen Institut des Stadt. Krankenhauses Miinchen-Harlaching. Inaugural Dissertation LMU Miinchen 26 Kyriakos M, Kempson R (1976) Inflammatory fibrous histiofltoma. Cancer 37: 1584-1606 2 Langace R, Delage C, Seemayer TA (1979) Myxoid variant of malignant fibrous histiocytoma. Ultrastructural observations. Cancer 43: 526-534 28 Lattes R (1982) Malignant fibrous histiocytoma. A review article. Am j Surg Pathol 6: 761-772 29 Lattes R (1982) Tumors of soft tissue, series 2, fascicle 1/ Revised. Atlas of UUDor pathology. Washington DC: Armed Forces Institute of Pathology, 130-145 30 Lee YS, Pho RWH, Nather A (1984) Malignant fibrous histiocytoma at site of metal implant. Cancer 54: 2286-2289

31 Limacher j, Delage C, Lagace R (1987) Malignant fibrous histiocytoma: Clinicopathologic and ultrastructural study of 12 cases. Am j Surg Pathol 2: 265-274 32 Magnussen B, Kindblom LG, Angervall L (1983) Enzyme histochemistry of malignant fibroblastic histiocytic tumors. A light and electron microscopic analysis. Appl Patholl: 223-240 33 Maximow A (1927) Bindegewebe und blutbildendes Gewebe. In: Handbuch der mikroskopischen Anatomie II (Herausgeber: v. M611endorf W) Springer, Berlin) 34 Meister P, Hahne N, Konrad E, Eder M (1979) Fibrous histiocytoma: an analysis of storiform pattern. Virchows Arch (A) 383: 31-41 35 Meister P, Nathrath W (1981) Immunohistochemical characterization of histiocytic tumours. Diagn Histopathol 4: 79-87 36 Meister P, Konrad EA, Nathrath W, Eder M (1980) Malignant fibrous histiocytoma: Histologic patterns and cell types. Path Res Pract 168: 193-212 37 Meister P, Wuensch PH, Konrad EA, Kirchner T (1980) Tumoren und tumorfarmige Veranderungen des Weichgewebes, Pathologe 2: 19-30 38 Merck C, Angervall L, Kindblom LG et a!. (1983) Myxofirbosarcoma. A malignant soft tissue tumor of fibroblastic-histiocytic origin. A clinicopathologic and prognostic study of 110 cases using multivariate analysis. Acta Pathol Microbiol Immunol Scand A (suppl) 91: 1-38 38. Merkow LP, Frich jC, Slifkin M, Kyriages CG, Pardo M (1971) Ultrastructure of fibroxanthosarcoma. Cancer 82: 372-383 39 Molenaar WM, Osterhuis AM (1985) The Rarity of Rhabdomyosarcomas in the Adult. A Morphologic and Immunohistochemical Study. Path Res Pract 180: 400-404 40 Nathrath WBj, Meister P (1982) Lysozyme (Muramidase) and alpha-l-antichymotrypsin as immunohistochemical tumor markers. Acta Histochem (suppl 25) 71: 69-72 41 Nathen (1920) Ein Fall von Fibroxanthosarcom. Frankfurt Zeitsch. Pathol 23: 471 42 Oberling C (1935) Retroperitoneal xanthogranuloma. Amj Cancer 23: 477 43 O'Brien jE, Stout AP (1964) Malignant fibrous xanthomas. Cancer 17: 1445-1455 44 Ozzello I, Stout AP, Murray MR (1963) Cultural characteristics of malignant fibrous histiocytomas and fibrous xanthomas. Cancer 16: 331-334 45 Permanetter W, Meister P (1984) Distribution of Lysozyme (Muramidase) and alpha-1-Antichymotrypsin in normal and neoplastic epithelial tissues: A survey. Acta histochem 74: 173-179 46 Pinkston jA, Seline I (1982) Postirradiation sarcoma (malignant fibrous histiocytoma) following cervix cancer. Cancer 49: 434-438 47 Reddick R, Michelitch H, Timothy (1979) Malignant soft tissue tumors: an electron microscopic study. Hum pathol 10: 327-343 48 Roholl PjM, Kleyne j, van Blockland M, van Unnik JAM (1986) Cell biological characterization of two malignant fibrous histiocytomas. Presentation: Internat!. Congr. v. lAP, Vienna 49 Rosai j (1981) Ackerman's Surgical Pathology. Mosby Co St. Louis 50 Russell W, Cohen-j, Enzinger F (1977) A clinical and pathological staging system for soft tissue sarcomas. Cancer 40: Is562-1570 51 Sobin L, Thomas L, Percy C, Hanson 0 (1978) A coded compendium of the international histological classification of tumors, WHO-Geneve 52 Stout AP, Lattes R (1967) Tumors of the soft tissues. (Atlas of tumor pathology, 2nd series, fasc. 1). Washington DC: Armed Forces Institute of Pathology

Malignant Fibrous Histiocytoma . 7 53 Taxy J, Battifora H (1977) Malignant fibrous histiocytoma. A clinicopathologic and ultrastructural study. Cander 40: 254-267 54 Tsuneyoshi M, Enjoji M (1980) Postirradiation sarcoma (malignant fibrous histiocytoma) following breast carcinoma. An ultrastructural study of a case. Cancer 45: 1419-1423 55 Tsuneyoshi M, Enjoji M, Shinchava N (1981) Malignant fibrous histiocytoma. An electromicroscopic study of 17 cases. Virchows Arch (Pathol Anat) 394: 135-145

56 Tsuneyoshi M, Daimaru Y, Enjoji M (1984) Malignant hemangiopericytoma and other sarcomas with hemangiopericytoma-like pattern. Path Res Pract 178: 446-453 57 Weiss SW (1982) Malignant fibrous histiocytoma. A reaffirmation. Am J Surg Pathol 6: 773-784 58 Weiss SW, Enzinger FM (1978) Malignant fibrous histiocytoma: An analysis of 200 cases. Cancer 41: 2250-2266 60 Wood GS, Beckstead JH, Turner MR, Kempson RL, Warnke RA (1985) Malignant fibrous histiocytoma tumor cells resemble fibroblasts. Am J Surg Pathol10: 323-335

Received February 9, 1987 . Accepted in revised form October 10, 1987

Key words: Malignant fibrous histiocytoma - Soft tissue tumors - Rhabdomyosarcoma - Histiocytic tumors - Sarcomas Prof. Dr. P. Meister, Institut f. Pathologie, Stadt. Krankenhaus Miinchen-Harlaching, Sanatoriumsplatz 2, 8000 Miinchen 80