Localized fibrous tumors of the pleura: correlation of histopathological, immunohistochemical and ultrastructural features

The Current Status of Solitary Fibrous Tumor: Diagnostic Features, Variants, and Genetics

Solitary fibrous tumor (SFT) is a fibroblastic mesenchymal tumor originally described in the pleura but now shown at almost every anatomic site. Histopathologically, SFT is characteristically a circumscribed neoplasm composed of variably cellular and patternless distributions of bland spindle and ovoid cells within prominent collagenous stroma and shows diffuse expression of CD34, but it has a broad spectrum of both morphology and of biologic behavior. Many different names (particularly hemangiopericytoma) were previously used in the course of our understanding of this neoplasm but are now subsumed under the term "SFT," and the putative cell of origin was debated. However, it is now recognized that SFT is a translocation-associated neoplasm, consistently associated with NAB2-STAT6 gene fusions arising from recurrent intrachromosomal rearrangements on chromosome 12q, and this translocation is a likely major contributor to its pathogenesis. While most SFT with classical morphologic features behave in an indolent manner and those with overtly malignant histologic features tend to be aggressive neoplasms that behave as high-grade sarcomas, the behavior of SFT is unpredictable, and it is important to be aware of the propensity for aggressive behavior in a minority of histologically classical SFT and to ensure adequate clinical follow-up. Surgical excision remains the treatment gold standard; while radiotherapy and conventional chemotherapeutic agents have only shown limited efficacy, further understanding of the molecular events underlying tumorigenesis may allow the development of novel targeted treatments. We review SFT, discussing the morphologic spectrum and variants, including malignant and dedifferentiated subtypes, clinicopathological aspects, recent molecular genetic findings, and the differential diagnosis.

Rare pleural tumors

Primary pleural tumors other than mesothelioma account for fewer than 1% of all lung cancers, and consequently they pose diagnostic and management challenges. Their treatment must be targeted toward the specific tumor type and is often quite different from the treatment for mesothelioma or metastases. Despite the best efforts at diagnosing and treating these tumors, the prognosis associated with some of the benign and many of the malignant variants of these tumors remains poor. In this review, we describe the radiologic and pathologic features of the less common primary pleural tumors and propose a diagnostic approach to their evaluation.

Thoracic solitary fibrous tumor: clinical and pathological diversity

Fourteen cases (13 pleural and one intrapulmonary) of solitary fibrous tumors (SFTs) (the so-called fibrous mesothelioma) were studied. The lesions occurred more in females (nine cases) than males (five cases). The age of patients ranged from 44 to 73 years old (median 60 years). The tumors presented as cough with or without blood-tinged sputum, exertional dyspnea, chest pain, nausea, body weight loss, fever, or as asymptomatic masses detected by routine chest radiograph. Two patients with huge (tumor larger than 20 cm) malignant tumors had accompanying pleural effusion and one associated with hypoglycemia. Ten benign tumors measured 2-11 cm (median size 7 cm) while the remaining four histologically malignant ones measured 20-30 cm in size. All of them were well circumscribed and thinly encapsulated. Hemorrhage and necrosis were more frequently seen in the malignant tumors. Histologically, these lesions were characterized by 'patternless pattern' with occasional hemangiopericytic features (three cases). The tumor cells were all immunoreactive for vimentin, CD 34, and focally actin-positive in one case, but not for keratin, desmin, S-100 protein, carcinoembryonic antigen, alpha 1-ACT and F VIII-related antigen, supported a primitive mesenchymal origin. p53 protein was expressed in two of the malignant cases. Proliferating cell nuclear antigen stain was positive with 50 and 80% of the labeling index in the benign and malignant tumors, respectively, but retinoblastoma gene protein was negative in all tumors. This analysis confirmed the relationship between histological malignant SFTs and tumor size, cellularity, mitotic activity, necrosis and tumor suppressor gene expression. However, the clinical behavior was unpredictable. Complete respectability seemed to be the most important indicator of clinical outcome in the less aggressive tumors.

Solitary fibrous tumour of the prostate

Solitary fibrous tumours are rare, benign neoplasms that are most commonly found in the pleura and less commonly on other serosal surfaces. Their cell of origin and aetiology are uncertain. A case of solitary fibrous tumour of the prostate is presented. We believe this to be the first case of this lesion to arise in this gland. Solitary fibrous tumours of the prostate may be confused with granulomatous prostatitis or carcinoma as all three may present with a nodule on rectal examination and appear as a hypoechoic nodule on transrectal ultrasound.

Extrapericardial solitary fibrous tumour of the pericardium

Solitary fibrous tumour (SFT) occurs most commonly in the pleura and is extremely rare in the pericardium. The authors report a case of a 60-year-old man in whom a large mediastinal mass was accidentally discovered. Computed tomography showed involvement of the left anterosuperior mediastinum with displacement of the trachea, large vessels and oesophagus; histopathological findings after complete resection of the neoplasia demonstrated an SFT of the pericardium, the first reported case with extrapericardial pattern of growth. A review of the literature on SFTs of the pericardium is provided.

[Localized fibrous tumor in the parenchyma. Report of 2 cases, one of them multiple and bilateral]

Localized fibrous tumor is an uncommon neoplasm that is usually located in the visceral pleura. Histologically these tumors are composed of randomly arranged fascicles or networks of fusiform cells, among which there is a varying amount of collagen. Most authors consider that these cells originate in submesothelial mesenchymal cells. The condition is normally silent, though hypoglycemia, hypertrophic osteoarthropathy or other symptoms sometimes result. The treatment of choice is total resection and imaging techniques are extremely helpful for establishing surgical strategy, even though surgery is often performed before a histopathologic diagnosis is available. We present 2 patients with intrapulmonary fibromas that were histologically identical to localized fibrous pleural tumors. These tumors are rarely found in the parenchyma and multiple bilateral presentation is exceptional, having been described only once in the literature. One of our patients had a single pulmonary node that happened to be noticed on an X-ray. The other had multiple bilateral nodes that required several surgical procedures; the intraparenchymatous location for this type of tumor has not been described to date. We discuss clinical, therapeutic and histopathological aspects of these tumors and review the literature.

Smooth muscle tumours presenting as pleural neoplasms

Five smooth muscle tumours presenting as pleural neoplasma are presented. The patients were three women and two men aged between 21 and 69 years (mean = 45 years). Clinically, one patient presented with chest pain, one with empyema and the other three were asymptomatic. Two of the tumours were located in the left side of the chest cavity and three in the right side. In four cases, the lesions presented as solitary pleural-based masses that varied in size from 10-18 cm in greatest dimension: in two of these cases, involvement of the diaphragm was present in addition to the pleural involvement. In one case, the tumour was seen to totally encase the right lung simulating the growth pattern of malignant mesothelioma. Histologically, three cases displayed an atypical spindle cell proliferation with marked cellular pleomorphism, mitoses and areas of hemorrhage and necrosis. The other two cases were characterized by a bland-appearing smooth muscle proliferation of uncertain malignant potential composed of elongated cells with a moderate amount of eosinophilic cytoplasm and cigar-shaped nuclei, lacking significant nuclear pleomorphism or mitotic activity. Immunohistochemical studies showed strong positivity for alpha-smooth muscle actin in all cases, and for desmin in four of five cases, and a focal positive reaction for keratin in one case. Ultrastructural examination in one of the high-grade tumours showed features of smooth muscle differentiation. Three of the patients were treated by complete surgical excision while, in the other two patients, the lesions were incompletely resected.(ABSTRACT TRUNCATED AT 250 WORDS)

Solitary fibrous tumour of the thyroid: clinicopathological, immunohistochemical and ultrastructural study of three cases

We describe three cases of solitary fibrous tumour (SFT) arising from thyroid stroma. Grossly, the tumours were clearly delimited but only partly encapsulated. The following histomorphological growth patterns were observed: bundles of cells in storiform configuration; non-structured bundles; prevalence of fibrous matrix; highly cellular, non-structured; prevalence of loose, non-structured extracellular substance; cellular proliferation and vascular spaces in a haemangiopericytic configuration and a lipomatous component. Immunohistochemical investigation demonstrated intense, diffuse vimentin positivity and focal, less intense actin positivity in all three cases. At electron microscopy we observed a primitive cell of mesenchymal type, with cytoplasm poor in organelles and rich in filaments; this cell sometimes presented differentiation characteristics. SFT is at present the most correct term for the lesions presented here despite some morphological characteristics which differ from cases reported in the literature.

Giant intrapericardial solitary fibrous tumor

A 60-year-old man with a large pericardial effusion was found to have a giant intrapericardial solitary fibrous mesothelioma firmly attached to the ascending aorta and pulmonary trunk. Nine months after excision of the mass the patient is free from symptoms and signs of tumor recurrence. Solitary fibrous mesothelioma is a rare benign tumor and its excision is curative; however, because of the lack of information on its long-term behavior, close noninvasive follow-up of this patient is necessary.