Solitary fibrous tumors of soft tissue. A clinicopathologic and immunohistochemical study of 12 cases

Desmoplastic fibroblastoma (collagenous fibroma)

Desmoplastic fibroblastoma is a vary rare subcutaneous proliferation. We describe a case of desmoplastic fibroblastoma in a 24-year-old Korean woman who presented with a 2.5 cm solitary and firm nodule on her back which had been present for 3 months. Histologic studies showed a well demarcated subcutaneous tumor composed of stellate or spindle shaped cells embedded in hypovascular fibrous or fibromyxoid stroma. No mitotic figures, calcification, or necrosis were observed. The stellate or spindle shaped cells were positive for vimentin. The stroma stained positively with Alcian blue and Masson trichrome. S-100 protein, actin, desmin, and elastic fiber stains were all negative in the stellate or spindle shaped cells. There has been no recurrence or metastasis of the tumor over an 18-month follow-up.

Solitary fibrous tumor of the meninges: two new cases and review of the literature

BACKGROUND

Solitary fibrous tumor (SFT), a mesenchymal neoplasm originally described in the pleura has been more recently reported to arise in a number of other sites, including the meninges. Nowadays immunohistochemistry facilitates the otherwise problematic differential diagnosis with regard to other benign and malignant spindle cell neoplasms of the central nervous system.

METHODS

Two recently treated cases of meningeal SFT (one craniospinal, one spinal) are presented and discussed in the light of the present knowledge and a review of the literature.

RESULTS

Total resection was followed by complete recovery and both patients are presently asymptomatic and without evidence of disease. The microscopic and immunohistochemical profiles (CD 34, vimentin positive; S-100, EMA negative) were consistent with those of previously reported cases.

CONCLUSIONS

The majority of SFTs behave in a benign fashion and do not recur unless subtotally resected. Malignant variants may account for up to 37% of SFTs in other locations but have never been reported to occur in the meninges. Meningeal SFTs are to be considered a new pathological entity. Wider use of immunohistochemical screening should enable the determination of their real incidence; larger series and longer follow-up will provide conclusions about their treatment and prognosis.

Solitary fibrous tumour of the forearm. A rare tumour in an atypical site

Solitary fibrous tumour (SFT) is a rare spindle cell neoplasm that usually arises from serosal surfaces. Although it is now increasingly recognized in extra-serosal locations, only two previous cases of SFT arising in an extremity have been reported. We describe another such case and review the literature regarding extra-serosal SFT.

Solitary fibrous tumor of the oral cavity: an uncommon location for a ubiquitous neoplasm

Solitary fibrous tumor is an uncommon soft tissue tumor initially reported in the pleura but recently described in other sites of the body. To date, only 5 examples of oral solitary fibrous tumor have been reported. Here, we describe 2 additional cases of this tumor in the oral cavity. The tumors were composed of small to medium-sized spindle cells with bland cytologic features; these cells were haphazardly arranged in highly cellular sheets or ill-formed fascicles as well as in hypocellular areas with hyalinized blood vessels. Both tumors contained blood vessels with a hemangiopericytomalike appearance and expressed vimentin, CD34, and CD99. One case was also strongly positive for bcl-2. The diagnosis of solitary fibrous tumor may be difficult inasmuch as it shares a number of histologic features with other soft tissue tumors. Awareness of its occurrence in the oral cavity is important so that confusion with other spindle cell neoplasms can be avoided.

Intramuscular solitary fibrous tumor: a clinicopathological case study

We present a case of extrapleural solitary fibrous tumor arising within the muscle, an unusual and hitherto-undescribed tumor lesion. A 42-year-old woman presented a painless mass in her left thigh. The lesion was depicted as an intramuscular mass that enhanced on both CT and MRI, showing quite rich tumor vascularity. The histological features of the tumor were spindle cell proliferation with various histological patterns, typical fibrocollagenous background, and positive immunoreactivity for CD-34.

Solitary fibrous tumor of the oral cavity: report of a case

A case of benign solitary fibrous tumor of the oral cavity is reported. The tumor occurred in the buccal mucosa of a 34-year-old woman. The surgically removed tumor was 1.5 x 1.2 x 1.0 cm in size and well circumscribed. Histologically, the tumor was composed of spindle-shaped cells that were predominantly arranged haphazardly. Hemangiopericytoma-like areas and collagenous areas were also noted. Immunohistochemically, the tumor cells were positive for CD34 and vimentin. To our knowledge, this is only the second report of solitary fibrous tumor involving the oral cavity.

Childhood desmoplastic fibroblastoma (collagenous fibroma) with a 12-year follow-up

We report the first case of a childhood desmoplastic fibroblastoma (collagenous fibroma). The tumor was located in subcutaneous tissue of the left buttock in a 5-year-old boy. No recurrence has been observed after 12 years, the longest follow-up available.

Atypical and malignant solitary fibrous tumors in extrathoracic locations: evidence of their comparability to intra-thoracic tumors

Solitary fibrous tumor (SFT), first described as a pleural lesion, has been reported at numerous extrathoracic sites over the past 10 years. About 10% to 15% of intrathoracic SFTs are histologically or clinically malignant, but such cases have very rarely been described at other locations. Among 92 cases of extrathoracic SFT in our files, we identified 10 that either had recurred (2 cases) or had a least one atypical histologic feature (8 cases). The ten tumors occurred in five men and five women, 32 to 81 years old (median 56), measured 1.9 cm to 20 cm (median 11.5 cm), and were located in the abdomen/pelvis (4 cases), retroperitoneum (3 cases), groin, trunk, and upper arm. Nuclear atypia (8 cases), markedly increased cellularity (6 cases), areas of necrosis (4 cases), and greater than 4 mitoses/10 HPFs (3 cases) were seen in addition to the typical histologic features of SFT. Six tumors had at least two of these atypical histologic features. Nine cases were positive for CD34, six were positive for O-13, and one was focally positive for smooth muscle actin. Eight were excised completely. Subsequent follow-up revealed tumor relapse in eight cases (follow up 6-180 months, median 24). Four patients had local recurrence at 12 to 168 months. Distant metastasis developed at 1 to 6 years in five cases with spread to lung (2 cases), liver (4 cases), and bone. Metastasis or local recurrence developed within 2 years in five patients. To date, no patient has died of their tumor. These findings demonstrate that nuclear atypia, hypercellularity, greater than 4 mitoses/10 HPFs, and necrosis may be seen in up to 10% of extrathoracic SFTs, and are associated with, but are not by themselves predictive of, aggressive clinical behavior. In addition, our findings confirm that the behavior of extrathoracic SFTs is unpredictable, entirely comparable to that of their better known pleural counterparts, and confirm that patients with SFTs in all locations require careful, long-term follow up. It is probably unwise to regard any such lesion as definitely benign.

Perineurial malignant peripheral nerve sheath tumor (MPNST): a clinicopathologic, immunohistochemical, and ultrastructural study of seven cases

Most malignant peripheral nerve sheath tumors (MPNST) are schwannian in nature. The pathologic features of MPNST with perineurial cell differentiation remain to be characterized. To determine the clinicopathologic, immunohistochemical, and ultrastructural characteristics of perineurial MPNST, 121 MPNST from the Mayo Clinic Tissue Registry were examined. Of these 23 spindle cell tumors with long processes disposed in whorls or storiform patterns, features typical of perineurioma, were studied. On the basis of immunohistochemistry (epithelial membrane antigen+/S-100-), 5 perineurial MPNST were identified among 23 tumors selected. These and two previously characterized perineurial MPNST are the subject of this study. None of seven tumors was associated with NF-1. Patients included five males and two females ranging in age from 11 to 83 years (mean, 45.7 years). The tumors measured 1.5 to 30 cm (mean, 9.1 cm) and arose in the extremities (two), trunk (two), face (one), mediastinum (one), and retroperitoneum (one). Only one tumor was nerve associated (phrenic nerve). All tumors were surgically removed. No encapsulation or neurofibroma components were noted. Necrosis was seen in three lesions. Four tumors were classified as high-grade malignant and three as low grade. Mitotic indices varied from 1 to 85/10 high-power fields (median, 16). Immunoreactivities included epithelial membrane antigen (100%), vimentin (100%), Leu-7 (57%), and CD34 (14%). Stains for S-100 protein, muscle markers, and cytokeratin were nonreactive. Ultrastructurally, perineurial-like cells were noted in three tumors and cells intermediate between perineurial and Schwann cells in one. Four tumors recurred and two metastasized; no deaths of disease were noted at follow-ups of 28 to 98 months (mean, 66.9). In conclusion, 4% of MPNST show perineurial cell differentiation. An NF-1 association has yet to be described. Nerve involvement is infrequent. Their immunophenotype (epithelial membrane antigen+/S-100-) frequently indicates ultrastructural perineurial differentiation. The prognosis of perineural MPNST appears to be more favorable than that of conventional MPNST.

Solitary fibrous tumour of the tongue

Solitary fibrous tumour (SFT) is a neoplasm most often localised in the pleura and peritoneum. The tumour is composed of spindled fibroblastic cells arranged in a haphazard way. Recently SFT has been described in many locations. Only one case of oral SFT has been described in the cheek: this is the second case of an oral SFT located in the tongue. The differential diagnosis must be made from many soft tissue tumours. SFTs stain strongly, in almost all cases, for CD34.

Expression of bcl-2 oncoprotein in benign and malignant spindle cell tumors of soft tissue, skin, serosal surfaces, and gastrointestinal tract

An immunohistochemical study to determine the pattern of immunoreactivity for bcl-2 oncoprotein was performed in 380 spindle cell tumors of soft tissue, skin, serosal surfaces, and gastrointestinal tract. The cases studied included examples of benign, reactive spindle cell proliferations to benign and malignant spindle cell neoplasms, including nodular fasciitis (10), fibromatosis (5), dermatofibroma (10), dermatofibrosarcoma protuberans (18), Kaposi's sarcoma (15), spindle cell lipomatous tumors (24), benign and malignant smooth muscle tumors (35), neural/peripheral nerve sheath neoplasms (53), synovial sarcomas (70) solitary fibrous tumors of serosal surfaces and other sites (56), gastrointestinal stromal tumors (GIST) (47), and malignant undifferentiated fibroblastic spindle cell proliferations of soft tissue (37 cases). The results of bcl-2 staining was additionally correlated with CD34 immunoreactivity. Bcl-2 was uniformly negative in all cases of nodular fasciitis, fibromatosis, and dermatofibroma, as well as in benign and malignant smooth muscle proliferations. Strong positivity for bcl-2 was observed in all cases of spindle cell lipoma, dendritic fibromyxolipoma, Kaposi's sarcoma, solitary fibrous tumors, gastrointestinal stromal tumors, and in the spindle cell component of synovial sarcoma. With the exception of the last, there appeared to be a close correlation between the expression of bcl-2 and CD34 in these tumors. Strong bcl-2 positivity also was found, at least focally, in approximately one third of benign and malignant peripheral nerve sheath tumors, particularly in the better-differentiated (Antoni type A) areas. Sarcomas of fibroblastic type, including low-grade myxofibrosarcoma, malignant fibrous histiocytoma, and fibrosarcoma, showed variable expression of bcl-2 in the tumor cells. Our results appear to indicate that bcl-2 may have a wide distribution among benign and malignant spindle cell neoplasms. Strong expression of this marker in some of these conditions, particularly solitary fibrous tumor, gastrointestinal stromal tumors, and synovial sarcoma, may be of aid for differential diagnosis.

Collagenous fibroma (desmoplastic fibroblastoma): a clinicopathologic analysis of 63 cases of a distinctive soft tissue lesion with stellate-shaped fibroblasts

Sixty-three cases of collagenous fibroma (desmoplastic fibroblastoma) from the files of the Armed Forces Institute of Pathology were analyzed. These tumors occurred mostly in men (80%) with a median age of 50 years (range, 16 to 81 years). The lesions had a wide anatomic distribution and involved the arm (24%), shoulder girdle (19%), posterior neck or upper back (14%), feet or ankles (14%), leg (14%), hand (8%), and abdominal wall and hip (6%). The patients typically presented with a history of a painless, slowly growing mass, often of relatively long duration. The tumors ranged in size from 1 to 20 cm (median, 3.0 cm). The lesions were predominantly subcutaneous, but fascial involvement was common, and 27% of cases involved skeletal muscle. Gross examination typically showed an elongated, lobulated, or disc-shaped mass with a firm consistency and a homogeneous pearl-gray color. Histologically, the tumors often appeared well marginated on low-power examination, but most (78%) infiltrated fat or, less commonly, skeletal muscle. The lesional cells were relatively bland stellate and spindle-shaped fibroblasts separated by a collagenous or myxocollagenous matrix. Mitotic activity was absent or minimal. Some of the lesional cells had a myofibroblastic immunophenotype, as evidenced by focal reactivity for muscle-specific and alpha-smooth muscle actins. In a few cases, rare actin-positive cells were also positive for keratins. Desmin, S100 protein, and CD34 were not expressed. None of the 39 patients with follow-up (median, 11 years) developed a recurrence. Collagenous fibroma is a benign fibroblastic/myofibroblastic proliferation. The large size of some of these tumors coupled with slow growth and persistence favors a neoplastic process over a peculiar reactive proliferation. The differential diagnosis includes a variety of reactive and neoplastic fibroblastic lesions, most importantly fibromatosis and low-grade fibromyxoid sarcoma. Simple, conservative excision is the treatment of choice for collagenous fibroma.

Fibrosarcomatous ("high-grade") dermatofibrosarcoma protuberans: clinicopathologic and immunohistochemical study of a series of 41 cases with emphasis on prognostic significance

The fibrosarcomatous variant of dermatofibrosarcoma protuberans (FS-DFSP) represents an uncommon form of DFSP, in which the prognostic influence of the fibrosarcomatous component is still debated. We analyzed the clinicopathologic and immunohistochemical features in a series of 41 patients. Patient age ranged from 8 to 87 years (median, 48 years), and 19 patients were female. Twenty five lesions were seen on the trunk, 6 on the upper limbs, and 4 on the lower limbs, and five neoplasms were located in the head/neck region; in one case, exact anatomic site was unknown. Twenty seven tumors involved purely dermal and subcutaneous tissues, in 10 cases, deeper structures were also involved, 1 case arose in the breast, and, in 3 cases, it was impossible to define exact depth of the lesion. Preoperative duration ranged from 1 month to 60 years (median, 3 years). Twenty six tumors were excised locally with clear margins, 7 were treated by wide excision, 3 by incomplete excision, and, in 4 patients, the lesion was shelled out. In one case, exact treatment was unknown. In addition, radiotherapy was administered in three cases and chemotherapy in one case. Histologically, the lesions showed areas of typical, low-grade DFSP adjacent to fibrosarcomatous areas. In four cases, a previously ordinary DFSP recurred as pure fibrosarcoma, in two cases, local recurrence of FS-DFSP showed features of ordinary DFSP. Fibrosarcomatous change was more common in the primary (de novo) lesions than in recurrent lesions (3.6:1). Proportion of fibrosarcoma varied between < 30% in 6 cases to > 70% of tumor tissue in 21 cases. An abrupt transition between both components was seen in 19 cases. The fibrosarcomatous component showed focal necrosis in seven cases and showed a higher mitotic rate in comparison with ordinary DFSP areas (mean, 13.4 versus 2.3 mitoses in 10 high-power fields). Additional histologic features included progression to pleomorphic sarcoma in 2 recurrent cases, melanin-pigmented cells (Bednar FS-DFSP) in 1 case, focal myxoid change in 13 cases, plaque or keloidlike hyalinization in 3 cases, and myoid bundles and nodules in 9 cases. Immunohistochemically, tumor cells in DFSP areas stained positively for CD34, whereas, in FS-DFSP areas, only 15 out 33 cases were positive for CD34. Follow-up in 34 of 41 patients (mean, 90 months; median, 36 months) revealed local recurrence in 20 patients (58%) (recurrence occurred in 5 patients on two or more occasions). Metastases (5 lung, 1 bone, and 1 soft tissue) were seen in 5 patients (14.7%), and 2 patients have died of tumor to date (5.8%). Necrosis, high mitotic rate (> 10 mitoses per 10 high-power fields), and presence of pleomorphic areas in FS-DFSP tended to be related with poor clinical outcome, but no statistically significant association was detected. Fibrosarcomatous change in DFSP represents a form of tumor progression in DFSP and is associated with a significantly more aggressive clinical course than in ordinary DFSP, indicating a possible need for treatment intensification in such cases.

Solitary fibrous tumour: significance of p53 and CD34 immunoreactivity in its malignant transformation

AIMS

To clarify the association of p53 and CD34 expression with development of malignant solitary fibrous tumour we have studied 10 cases of solitary fibrous tumour arising in the pleura, retroperitoneum and pelvic cavity with clinicopathological features of malignancy.

METHODS AND RESULTS

Tumours were localized solid masses with or without necrosis in eight and they nearly totally occupied the pleural cavity in two. Basic histology of the tumours was the proliferation of spindle cells arranged in 'patternless' pattern or in interlacing bundles with nuclear atypia and mitotic activities of various degree. In two, high-grade foci were present within low or intermediate-grade tumours. Recurrent tumours also showed more atypical features than primary tumours in two. Immunohistochemical studies showed CD34 positivity in seven, but three of them showed marked diminution or complete loss of CD34 expression in high-grade foci or a recurrent tumour. Three high-grade cases showed totally negative staining for CD34. p53 was strongly expressed in cases with fatal outcome, clinical recurrence, nuclear atypia, high mitotic activity or local invasion, whereas almost negative in benign tumours.

CONCLUSIONS

Malignant solitary fibrous tumours may occur de novo or by transformation within benign or low-grade tumours and may be associated with p53 mutation. Although CD34 is a useful marker in the diagnosis of solitary fibrous tumour, one should bear in mind that its expression can be lost in high-grade tumours.

Dendritic fibromyxolipoma: clinicopathologic study of a distinctive benign soft tissue lesion that may be mistaken for a sarcoma

Twelve cases are described of a distinctive benign soft tissue lesion that may be mistaken for a sarcoma. The tumors occurred in 11 men and a woman aged 33 to 81 years (mean, 64 years), and measured from 2 to 11 cm in greatest diameter (mean, 6 cm). They were grossly described as soft, well-circumscribed, yellow-gray, with a mucoid cut surface. All cases were superficially located in the subcutis or muscular fascia of the head and neck region or the chest and back. Histologically, the tumors were characterized by a proliferation of spindle or stellate fibroblastic cells variably admixed with mature adipose tissue embedded in an abundant myxoid and collagenized stroma. The spindle and stellate fibroblastic cells were characterized by slender dendritic prolongations of their cytoplasm, which appeared to extend for short distances along connective tissue planes. Electron microscopy in two cases confirmed the dendritic nature of the fibroblastic cells, which showed elongated cytoplasmic processes lacking external lamina and displaying foci of pinocytotic activity. Immunohistochemical studies in 11 cases showed strong positivity of the spindle cells with vimentin, CD34 and bcl-2, and negative staining for smooth muscle actin, muscle-specific actin (HHF35), desmin, S-100 protein, keratin, and EMA. Because of their prominent myxoid stroma and relatively large size, some of these tumors were initially misinterpreted as low-grade sarcomas. Clinical follow-up in five cases, however, showed that the patients were alive and well without evidence of recurrence between 5 and 13 years (mean follow-up, 8 years) after simple local excision. The present cases appear to represent a distinctive form of benign soft tissue neoplasm that should be distinguished from myxoid liposarcoma and other benign and malignant myxoid tumors of superficial soft tissues.

Frequent expression of bcl-2 protein in solitary fibrous tumors

The distinction of solitary fibrous tumors from histologically similar neoplasms is often difficult because they rarely occur at a variety of extrapleural sites. CD34 immunoreactivity has recently been recognized to be an adjunct for the diagnosis of solitary fibrous tumors. However, it is now known that CD34 staining is not entirely specific for this entity. We evaluated 23 solitary fibrous tumors and 54 other spindle cell tumors often considered in the differential diagnosis for immunoreactivity using monoclonal antibodies directed against bcl-2 protein, which protects cells from apoptosis and CD34. The patients with solitary fibrous tumors comprised 11 men and 12 women, ranging in age from 35 to 85 years (mean, 57.6 years). Fourteen tumors arose in the pleura, four in the retroperitoneum, three in the superficial soft tissue and one each in the mediastinum and uterine cervix. Nineteen of 23 solitary fibrous tumors (83%), irrespective of tumor site, demonstrated diffuse cytoplasmic staining for bcl-2 protein. bcl-2 immunoreactivity was also observed in five of seven neurofibromas (71%), eight of 10 synovial sarcomas (80%) and one of three spindle cell lipomas (33%). CD34 immunoreactivity was present in all but one solitary fibrous tumor (96%), seven of seven neurofibromas (100%), three of three spindle cell lipomas (100%), five of five dermatofibrosarcomas (100%), three of three hemangiopericytomas (100%) and two of seven malignant fibrous histiocytomas (29%). To date, most of the pleural and extrapleural cases have not shown aggressive features. We suggest that bcl-2 protein can be used together with CD34 in the diagnosis of solitary fibrous tumor to distinguish this entity from other spindle cell neoplasms.

Solitary fibrous tumor of the liver: a clinicopathologic and immunohistochemical study of nine cases

Nine cases of primary solitary fibrous tumors of the liver are presented. The patients are 7 women and 2 men between the ages of 32 and 83 years (mean, 57.5 years). Clinically, palpable masses were detected during physical examination in five patients. Two patients presented with symptoms of cholecystitis, one with hematuria, one with periumbilical pain, and one with hypoglycemia. One patient was found to have an abdominal mass during follow-up evaluation for colonic carcinoma, whereas in one patient the tumor was an incidental finding at autopsy. Two patients were asymptomatic, and the tumor masses were detected during a routine physical examination. Grossly, the tumors varied in size from 2 to more than 20 cm in greatest dimension and were described as firm, white-to-gray, well or ill defined. Eight tumors were described as intraparenchymal lesions, two were grossly necrotic, and one tumor was attached by a pedicle to the liver capsule without infiltration into the liver parenchyma. Histologically, most of the tumors had a bland appearance with the classic short storiform (so-called patternless) pattern and absence of cellular atypia, mitoses and/or necrosis. However, in two cases, there was marked cellular atypia and mitotic figures varying from 2 to 4 mitoses per 10 high power field (hpf). Immunohistochemically, all the tumors showed a strong positive reaction against antibodies for CD-34 and vimentin. Follow-up information showed that two patients died within days of postsurgical resection of the tumor, whereas one was alive and well 1 year after initial diagnosis. No follow-up information was available for the other five patients. The cases herein presented highlight the ubiquitous distribution of this neoplasm and the similar clinical and histopathological features to those observed in serosal surfaces. Solitary fibrous tumors of the liver, although rare, need to be considered in the differential diagnosis of mesenchymal lesions of the liver.

Angiomyofibroblastomalike tumor of the male genital tract: analysis of 11 cases with comparison to female angiomyofibroblastoma and spindle cell lipoma

The clinicopathologic features and immunoprofile of 11 cases of an uncharacterized male genital tract tumor with features of vulvovaginal angiomyofibroblastoma (AMF) and spindle cell lipoma (male AMF-like tumor) are described. The lesions presented as a mass involving the scrotum (six cases) or inguinal region (five cases) in males ranging in age from 39 to 88 years (median 57). The tumors were superficially located and well-marginated and ranged in size from 2.5 to 14 cm (approximate mean 7 cm). Microscopically, they were composed of tapered spindled cells proliferating between numerous small to medium-sized vessels. Epithelioid appearing stromal cells were a focal finding in four cases. Mitotic activity was minimal with no abnormal mitotic figures identified. Mild nuclear atypia was identified in two cases. The tumors possessed an acid mucopolysaccharide-rich, finely collagenous stroma. A small quantity of intralesional fat was present in six cases. Tumor cells exhibited immunoreactivity for vimentin (seven of seven cases), progesterone receptor protein (five of seven cases), CD34 (four of eight cases), estrogen receptor protein (three of seven cases), desmin (three of eight cases), muscle-specific actin (three of eight cases), and smooth-muscle actin (two of eight cases) but not for S-100 protein. One of seven patients with follow-up after simple excision had recurrent/persistent disease. The male AMF-like tumor is a soft-tissue neoplasm of the male genital tract that shares clinicopathologic features and a proposed perivascular stem cell derivation with both the female angiomyofibroblastoma and spindle cell lipoma.

Pleomorphic hyalinizing angiectatic tumor of soft parts

A case of recently described pleomorphic hyalinizing angiectatic tumor (PHAT) of soft parts is reported. The subcutaneous solid tumor arising in the axilla of a 58-year-old man was histologically characterized by sheets of mitotically inactive oval and pleomorphic cells, intranuclear cytoplasmic inclusions, and clusters of ectatic vessels with perivascular hyalinization. Mono- and multinucleated giant cells were also present. A hemangiopericytoma-like pattern of vascularity, pseudovascular spaces, stromal collagen with degenerative changes, and immunoreactivity for CD34 were observed. Since these features were very similar to those of solitary fibrous tumors of various sites and newly categorized giant cell angiofibroma, it is considered that PHAT, solitary fibrous tumor, and giant cell angiofibroma may be in the same family of tumor. The tumor was diploid with a low S-phase fraction. The patient was well with no evidence of disease for 23 months.

Solitary fibrous tumor of the prostate

A case of solitary fibrous tumor of the prostate is reported. A 42-year-old man had been complaining of difficult voiding and constipation for 8 years. Urological and radiological examinations showed a large prostatic mass, and a total cystectomy and prostatectomy were performed. The tumor was 14 x 13 x 11 cm in size, solid with a fibromuscular capsule, and gray-tan in color. Histologically, the tumor was composed of short spindle-shaped and polygonal cells with mild to moderate nuclear atypia, predominantly arranged in the so-called 'patternless pattern' in a fibrocollagenous background. Mitoses were occasionally seen. Vascular invasion was also observed. Immunohistochemically, these cells were strongly positive for CD34 and vimentin, and occasionally for desmin. The maximum Ki-67 labeling index of the tumor cells was 4.5%. These findings are consistent with a solitary fibrous tumor. To our knowledge, this is the first report of a solitary fibrous tumor of the prostate in the English medical literature.

Solitary fibrous tumor of the skin

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that most commonly involves the pleura, but is increasingly more often observed in extrapleural locations. A 37-year-old woman presented with an SFT involving the skin and subcutaneous tissue of the scalp. Histologically, SFT is well circumscribed and composed of uniform spindle cells arranged in interlacing fascicles. It exhibits alternating hypercellular and hypocellular areas with abundant thick, often keloid-like, hyalinized collagen. Hemangiopericytoma-like areas are frequently prominent. Immunohistochemical markers for smooth muscle, neural, and epithelial differentiation are negative, but generalized positivity for CD-34 is characteristic. Because of the expanding spectrum of anatomic involvement of SFT, it is not surprising that on rare occasions this tumor may involve the skin.

Solitary fibrous tumor of urinary bladder: report of two cases

The clinical and pathologic features of two cases of solitary fibrous tumor arising from urinary bladder wall are described. To our knowledge, solitary fibrous tumors have not been previously reported at this site. Both tumors showed typical histologic features of solitary fibrous tumor, were CD34 immunostain positive and pursued a benign clinical course on short term follow-up.

Angiomyofibroblastoma of the female genital tract: analysis of 17 cases including a lipomatous variant

The clinicopathological and immunohistochemical profile of 17 cases of angiomyofibroblastoma (AMF) arising in the genital tract of females is reported. The lesions usually presented as painless masses and were located in the superficial vulvar region (15 cases), canal of Nuck (one case), and perineum (one case) in women ranging in age from 38 to 60 years (median, 46 years). The tumors were well delineated and ranged in size from 2 to 8 cm in greatest dimension. Microscopically, they were composed of spindled and epithelioid mesenchymal cells arranged in cords and nests preferentially arrayed around numerous small to medium-sized vessels. Mitotic activity ranged from 0 to 7 mitoses per 50 high-power fields (HPF) with no abnormal mitotic figures. Minimal nuclear atypia was appreciated. Intralesional fat was present in 12 cases and in two of these cases constituted most of the tumor (lipomatous variant of AMF). Tumor cells expressed vimentin (five of five cases), estrogen receptor protein (six of six cases), progesterone receptor protein (five of six cases), desmin (six of eight cases), CD34 (one of six cases), and smooth muscle actin (one of seven cases). None of the eight women with follow-up of up to 25 years (mean, 7.8 years) after simple excision developed a recurrence. This study confirms the benign nature of AMF, broadens its morphological spectrum to include a lipomatous variant, and proposes an origin from a perivascular stem cell that is capable of myofibroblastic and fatty differentiation.

Fibrohistiocytic differentiation in subcutaneous fatty tumors. Study of spindle cell, pleomorphic, myxoid, and atypical lipoma and dedifferentiated liposarcoma cases composed in part of CD34+ fibroblasts and FXIIIa+ histiocytes

Subsets of dendritic cells, fibroblasts which express the human progenitor cell antigen CD34 or histiocytes which express coagulation factor XIIIa (FXIIIa), are present in fat and in collagenous connective tissue. As components of the microvascular unit, these fibrohistiocytic cell subsets may interact during stromal remodeling, repair, and neoplasia. We studied white fat and subcutaneous fatty tumors to determine if CD34 and/or FXIIIa+ "fibrohistiocytic" dendritic cell subsets are involved in their morphogenesis. Three lipomas (L), 1 intramuscular lipoma (IL), 1 myxoid lipoma (ML), 2 pleomorphic lipomas (PL), 2 spindle cell lipomas (SCL), 8 angiolipomas (AN) in 4 patients, 1 atypical lipoma/well-differentiated liposarcoma (AL), 1 de novo dedifferentiated liposarcoma (DL), and 1 recurring atypical myxoid signet ring lipomatous tumor were examined for CD34, FXIIIa and in some cases for CD31, desmin, Ki 67, or S-100. Normal fat has scattered CD34+ dendritic cells and small FXIIIa+ dendritic histiocytes among variably S-100+ adipocytes. The CD34 and FXIIIa+ dendritic cells are more numerous near vessels and within fibrovascular septae. In L and IL, CD34 and FXIIIa+ dendritic cells are activated and some adipocytes express CD34. Mesenchymal areas of SCL, PL, ML, and AL and DL are composed of CD34+ dendritic cells with CD34+ but FXIIIa-negative floret cells in PL or atypical cells in AL and DL. FXIIIa+ dendritic cells are numerous in these lesions, comprising 30-40% of cells in SCL and PL, and 50% in ML, AL, and DL. AN have focal CD34+ interstitial cells and plump FXIIIa+ cells that in one case resembled multivacuolated lipoblasts. The myxoid signet ring lipomatous tumor was CD34 negative with few FXIIIa+ cells. We conclude that subsets of CD34+ and FXIIIa+ dendritic microvascular cells are present in normal fat and proliferate together in various types of lipomas and in at least some dedifferentiated liposarcomas.

Malignant cartilaginous tumors of the mediastinum: clinicopathological study of six cases presenting as extraskeletal soft tissue masses

Cartilage and bone-forming tumors of the mediastinum are extremely rare neoplasms with very few cases having been reported in the literature. We studied six cases of primary malignant cartilaginous tumors presenting as extraskeletal soft tissue masses in the posterior mediastinum. The patients were five women and one man aged 11 to 63 years (median, 31 years). Histologically, the lesions showed a spectrum of features that ranged from mesenchymal chondrosarcoma, to extraskeletal myxoid chondrosarcoma, to moderately well to poorly differentiated chondrosarcoma. In all cases, the lesions presented as well-circumscribed tumor masses centered in the soft tissues in the posterior mediastinum without radiographic evidence of origin from bone. Because of their relatively small size, good circumscription, focal areas of calcification, and posterior mediastinal location, the preoperative clinical diagnoses included benign neurogenic tumor and neuroblastoma. All of the lesions were treated by complete surgical excision, followed in two cases by postoperative radiation therapy. Clinical follow-up was available in five cases: two patients with mesenchymal chondrosarcoma presented with local recurrence after 3 and 7 years, one developed metastases to the sacrum 8 years after initial diagnosis and died, and one was alive and well without evidence of disease after 6 years. The patient with myxoid chondrosarcoma of the posterior mediastinum developed bilateral pulmonary metastases 10 months after surgery and has been lost to follow-up since. Our findings reinforce previous observations on the occurrence of extraskeletal cartilaginous tumors in the mediastinum and indicate that these tumors can show a propensity for local aggressive behavior with high recurrence rate and a definite potential for distant metastases. Such tumors should be considered in the differential diagnosis of malignant neoplasms presenting as a soft tissue mass in the posterior mediastinum.

Solitary fibrous tumor of the spinal cord

We report a case of primary solitary fibrous tumor occurring in the intramedullary thoracic spinal cord in a 47-year-old man. The tumor predominately consisted of spindle cells separated by abundant collagen; a few areas of hemangiopericytomatous morphology were also present. The diagnosis was confirmed by immunohistochemistry and electron microscopy. The tumor was reactive to vimentin and CD34 but was negative for glial fibrillary acid protein (GFAP), S-100, smooth muscle actin, epithelial membrane antigen, HMB-45, myelin basic protein, and keratin; ultrastructural examination showed fairly undifferentiated cells within a collagenous matrix, few tight junctions, and sparse extravascular basement membrane. The occurrence of this tumor within the spinal cord parenchyma and in other extraserosal sites emphasizes the current belief that solitary fibrous tumors arise from mesenchymal tissues and are not restricted to the pleura and other serosal surfaces. Furthermore, solitary fibrous tumor is an entity that must be considered in the differential diagnosis of spindle cell central nervous system neoplasms.

bcl-2 expression in pleural and extrapleural solitary fibrous tumours

This study evaluated the immunoreactivity for bcl-2, a molecule involved in the control of programmed cell death, in cases of pleural (14) and extrapleural (2) solitary fibrous tumour (SFT), malignant mesotheliomas of different histological types, and a variety of extrapleural CD34-positive and CD34-negative spindle-cell tumours. In all SFTs, strong and diffuse immunostaining was demonstrated with anti-bel-2 antibody, sharply contrasting with the complete lack of staining observed in all mesotheliomas. The specificity of immunodetection of bcl-2 in SFT was confirmed by immunoblot analysis, showing a band consistent with the bcl-2 protein. At extrapleural locations, strong bcl-2 immunoreactivity was observed in Schwannoma (2/3 cases), synovial sarcoma (4/4 cases), and all cases of CD34-positive gastrointestinal stromal tumour (GIST; 10/10 cases). Most sarcomas were bcl-2-negative. Lack of bcl-2 expression was demonstrated in tumours which can pose problems in the differential diagnosis of SFT and can exhibit haemangiopericytoma-like features, including haemangiopericytoma (3 cases), dermatofibrosarcoma protuberans (16 cases), and deep-seated fibrous histiocytoma (3 cases). The constitutive expression of bcl-2 in SFT widens the spectrum of available markers for these tumours, providing a useful adjunct to their differential diagnosis in difficult cases at pleural and extrapleural sites, and contributing to the understanding of their histogenesis and molecular pathogenesis.

Benign fibromatous tumors of the testis and paratesticular region: a report of 9 cases with a proposed classification of fibromatous tumors and tumor-like lesions

Benign intrascrotal fibrous proliferations are uncommon, with most arising from the paratesticular region and falling into the category of so-called fibrous pseudotumor. We describe two neoplastic forms of benign fibrous tumor of the testis and its adnexa: fibroma of gonadal stromal origin and fibroma of the testicular tunics. Three patients with gonadal stromal fibroma were 28, 33, and 35 years of age and presented with painless masses. The tumors were circumscribed, intratesticular, yellow-white or white lesions 0.9 to 4.0 cm in diameter and had microscopic features identical to those of the ovarian fibroma. Immunohistochemically, the tumor cells were strongly positive for vimentin (3/3 cases), focally positive for actin and desmin (2/3 cases) and negative for S-100, keratin, and CD34 (3/3 cases). Six fibromas of the testicular tunics arose in patients 22, 34, 60, 68, 70, and 74 years old and were also asymptomatic masses. Four of them were circumscribed, whorled, white masses arising from the tunica albuginea with variable areas of myxoid change; one was pedunculated and grew exclusively into the cavity of the tunica vaginalis, whereas the other three at least partially extended into the testis as well. The other two tumors were unattached to the tunica albuginea and presented as circumscribed, white-tan paratesticular masses, partially covered by tunica vaginalis. Microscopically, the tumors were slightly to moderately cellular, with bland spindle or stellate cells lying in a myxoid or collagenous stroma with prominent vessels. The two paratesticular tumors had features typical of solitary fibrous tumor. Immunohistochemically, the fibromas of the testicular tunics were negative for S-100, keratin, and desmin. Focal, weak reactivity for actin was present in one case. CD34 was positive in three cases; in the two tumors resembling solitary fibrous tumors it was strong, and in the other it was focal and was limited to the region just below the tunica vaginalis. Eight tumors were treated by radical orchiectomy and one by excision of the mass alone. The outcome was benign in the seven cases in which followup information is available.

Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors

The human hematopoietic progenitor cell antigen (CD34) recently was shown to react with a variety of nonhematopoietic tissues and their tumors, including vascular endothelium, dendritic interstitial fibroblastic cells, and endoneurial cells as well as with the neoplastic cells in a variety of mesenchymal neoplasms of unknown etiology, such as Kaposi's sarcoma, dermatofibrosarcoma protuberans, epithelioid sarcoma, gastrointestinal stromal tumors, and solitary fibrous tumors. Additionally, it has been claimed that normal adipocytes may also react with this antibody. We studied a series of 90 lipomatous lesions to examine the pattern of immunoreactivity of the CD34 antigen in adipose tissue neoplasms. The study included 14 lipomas, 19 angiolipomas, 4 atypical lipomas, 18 spindle cell lipomas, 3 renal angiomyolipomas, 1 intramuscular lipoma, and 31 liposarcomas. Immunostains identified a network of CD34+ spindle cells admixed with the adipose tissue elements in all cases of lipoma, angiolipoma, angiomyolipoma, intramuscular lipoma, and well-differentiated lipoma-like liposarcoma. Additionally, the spindle cell component in all cases of spindle cell lipoma were strongly positive for this antigen. Atypical, stellate spindle cells and multinucleated "floret" cells in all cases of atypical lipoma as well as in six of 12 cases of well-differentiated lipoma-like liposarcoma of deep soft tissue were also positive for CD34. Scattered spindle cells in all cases of myxoid liposarcoma and in one case of round cell liposarcoma, as well as the sarcomatous component in one case of "dedifferentiated" liposarcoma, were strongly positive for this antigen. The round cells in myxoid liposarcoma and round cell liposarcoma, the signet-ring and multivacuolated lipoblasts in well-differentiated liposarcoma, and the pleomorphic atypical cells in pleomorphic liposarcoma were uniformly negative. The results of this study appear to indicate that lipomatous tumors may harbor a population of CD34+ interstitial dendritic spindle cells. Overgrowth or clonal expansion of this dendritic cell subpopulation may account for the development of spindle cell lipomas and for the spindle cell component in some cases of "dedifferentiated" liposarcoma.

An unusual soft tissue tumor with features of angiomatoid malignant fibrous histiocytoma composed of bimodal CD34 and factor XIIIa positive dendritic cell subsets. CD34 and factor XIIIa in angiomatoid MFH

CD34 and factor XIIIa (FXIIIa) antibodies delineate subsets of embryonic dendritic stromal stem cells that persist in adult mesenchyme. CD34 stains interstitial and adventitial dendritic cells that may function as multipotential precursor cells. FXIIIa+ dendrophages are tissue histiocytes active in tissue repair. Angiomatoid malignant fibrous histiocytoma (AMFH) is an enigmatic fibrohistiocytic tumor with limited vascular features. We examined an unusual soft tissue tumor from the nasolabial subcutis of a 57 year old man that showed histologic features of AMFH. Most of the tumor cells expressed CD34. 10-30% of the tumor cells were FXIIIa+ dendrophages. Sinusoidal areas were largely composed of FXIIIa+ cells that also expressed HLA-DR and CD68 suggesting macrophage differentiation. CD31 and Factor VIII antigen highlighted capillaries and single cells among the CD34+ tumor cells. The vessels had actin+ myopericytes and there were single actin+ tumor cells. Electron microscopy showed primitive dendritic cells and fewer histiocyte-like cells. The Ki 67 index was 15% including both FXIIIa+ and CD34+ cells. The patient is disease free three years after wide excision. We conclude that this AMFH-like neoplasm is a fibrohistiocytic tumor in which CD34+ fibroblast-like precursors and FXIIIa+ tissue dendrophages combine to build both sinusoidal tissue with endothelial and macrophage elements as well as capillary vascular tissue that is invested with myopericytes. Study of additional AMFH lesions from this standpoint is desirable.

Myxoid dermatofibrohistiocytoma: an indolent post-traumatic tumor composed of CD34+ epithelioid and dendritic cells and factor XIIIa+ dendrophages

Factor XIIIa+ dendrophages and CD34+ "deep dermal dendrocytes" are distinct subsets of embryonic dermal dendritic stem cells that persist in interstitial and adventitial sites in adult dermis. We encountered a unique myxoid dermal tumor composed of these two cell types. It arose after trauma to the thumb of a 49-year-old man and was locally excised. The patient is without recurrence at 18 months. The disc-shaped tumor was lobulated, yellow, and mucoid and involved the margins. A fibrillar myxoid stroma contained mast cells, wispy collagen with medium-to-small vessels, and loosely deployed small eosinophilic tumor cells. The tumor cells were amitotic and had oval or bean-shaped, bland nuclei; some cells were binucleated. The cells were epithelioid or dendritic with bipolar, stellate, and racquet-shaped cytosomes whose tapering cell processes blended with fibrillar collagen. Vacuolated epithelioid cells focally formed vessel-like luminal structure. All cells strongly expressed vimentin. Thirty percent of the tumor cells were elongated, dendritic factor XIIIa+ cells whose dendritic processes enshrouded mast cells or FXIIIa-negative tumor cells. A subset of the FXIIIa+ cells also expressed MAC387 and lysozyme. The other 70% of the cells were CD34+. Many CD34+ cells were epithelioid with strong membrane and vacuolar decoration. Some CD34+ epithelioid cells had globular cytoplasmic inclusions. Other CD34+ cells were dendritic with multipolar fibrobroblast-like cytosomes and weaker CD34+ membrane decoration. Actin and S-100 were negative. Ki 67 was expressed in 1% of the tumor cells. Double stains for CD34 and Ki 67 showed that both CD34+ cells and FXIIIa+ dendrophages were Ki 67+, as were many papillary dermal vessel endothelial cells. The composition of the tumor by mast cells, FXIIIa+ dendrophages, and CD34+ primitive cells recapitulates the dermal microvascular unit. We propose the descriptive term myxoid dermatofibrohistiocytoma (MD) for this novel tumor. It appears to be an unusual response by dermal dendritic cells, perhaps due to continued stimulation by post-traumatic cytokines. Clarification of its biology and nosology awaits identification and study of more cases.