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Solitary fibrous tumor of the oral cavity with a predominant leiomyomatous-like pattern: A potential diagnostic pitfall

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Abstract

The diagnosis of solitary fibrous tumor (SFT) is usually straightforward if the typical morphologic features, including a wide variety of growth patterns, are identified. We report the clinical, radiologic, and pathologic findings of a rare case of intraoral SFT which exhibited a predominant leiomyomatous-like appearance, closely reminiscent of a leiomyoma, at both incisional and excisional biopsy. Histologically, the tumor was composed predominantly of intersecting fascicles of eosinophilic spindle-shaped cells, variably set in a fibrous stroma. A focal hemangiopericytoma-like growth pattern with alternating hypercellular and hypocellular areas, as well as the deposition of dense keloid-type collagen, raising the suspicion of SFT, could be identified only after a careful examination of the whole tumor. Immunohistochemistry was helpful in confirming the diagnosis of SFT, revealing a diffuse staining of neoplastic cells for vimentin, CD34, bcl-2 protein, and, focally, CD99. Myogenic markers (α-smooth muscle actin, desmin, h-caldesmon) were not expressed.

The pathologist should be aware of this variant of intraoral leiomyomatous-like SFT to avoid a misdiagnosis of leiomyoma. The distinction of SFT from leiomyoma in the oral cavity is important to assure both correct treatment and prognostic information.

Introduction

Solitary fibrous tumor (SFT) is a relatively uncommon but distinct mesenchymal fibroblastic tumor originally described in the pleura. In the last two decades, there was increasing evidence that this tumor may arise ubiquitously from somatic and deep soft tissues, as well as from parenchymal organs [4], [5], [9], [10], [20], [23]. In the oral cavity, SFT may rarely occur, with about 80 cases reported so far [11], [17], [19]. The most commonly involved regions are: buccal mucosa, tongue, cheek, lips, gums, palate, and floor of the mouth [1], [11], [12], [13], [14], [17], [24]. Most patients have a history of a slow-growing, painless, sub-mucosal mass of variable size (from 1.5 to 7 cm in diameter) and duration [1], [12], [14], [17]. SFT can be clinically confused with a salivary gland tumor, lipoma, mucocele, vascular malformation, lymphoma, ameloblastoma, and abscess from dental infection [1], [12], [14]. Although the histologic diagnosis of SFT is straightforward in most cases, some difficulties may occasionally arise, especially due to the wide variability of growth patterns exhibited by this tumor. In this regard, some authors emphasize the most important criteria for a correct diagnosis of pleural and extrapleural SFT [5]: (i) tumor circumscription; (ii) bland-looking spindle- to ovoid-shaped cells; (iii) haphazard arrangement of neoplastic cells (patternless growth pattern) with focal storiform or fascicular pattern; (iv) alternating hypercellular and hypocellular areas; (v) rich vasculature with hemangiopericytoma-like pattern; (vi) perivascular hyalinization; (vii) thin and thick collagen fibers; and (viii) low (<4/10 HPF) mitotic index. In addition, a variable degree of myxomatous stromal changes, scattered multinucleated stromal giant cells, and numerous mast cells may also be present [1], [9], [23]. The above-mentioned morphologic features, although shared by all SFTs, are represented with considerable variability. The majority of SFTs are benign histologically. However, a small percentage of SFTs (5%) which exhibit hypercellularity, moderate to severe cellular pleomorphism, high mitotic activity (>4 mitoses per 10 high-power fields), necrosis, and/or infiltrative margins usually show an aggressive clinical course. However, some cases of “histologically benign” SFTs do recur or metastasize in about 10–15% of cases [10], [20], and, in contrast, “histologically malignant SFTs” occasionally behave in a benign manner [7], [10], [16]. Accordingly, the biologic behavior of SFT cannot be predicted in all cases, based on histopathologic features alone.

We herein report a rare case of SFT of the oral cavity, showing a predominant leiomyomatous-like appearance. Although it is known that rare cases of SFTs of the oral cavity may show, at least focally, leiomyoma-like areas [17], leading the pathologist to a misdiagnosis of leiomyoma [13], this potential diagnostic pitfall feature, to the best of our knowledge, has not yet been emphasized. The present case underlines the diagnostic difficulties encountered in the evaluation of incisional and excisional biopsies from a SFT of the buccal mucosa, which was initially confused with a leiomyoma. The correct diagnosis of SFT was achieved after a careful evaluation of all morphologic and immunohistochemical findings.

Section snippets

Clinical history

A 54-year-old Caucasian female presented a swelling of her left cheek. The lesion had been first noted 8 months before. Her medical history was unremarkable. On physical examination, an asymmetry on the left side of the face was noted. Oropharyngeal examination demonstrated a painless, nodular mass measuring 6 cm in maximum diameter in the left buccal mucosa. The lesion had a smooth surface and was firm in consistency. Neither regional lymphadenopathy nor regional cranial nerve deficits were

Conventional histology and immunohistochemistry

The surgical specimen was fixed in 10% buffered formalin, routinely processed, and embedded in paraffin. Sections (4 μm thick) were stained with hematoxylin and eosin. Additional sections were cut for immunohistochemical procedures. Immunohistochemical studies were performed with the labeled streptavidin–biotin peroxidase detection system using the Ventana automated immunostainer (Ventana Medical Sistem, Tucson, AZ). A large panel of antibodies were used: pancytokeratins (dilution 1:200), EMA

Pathologic and immunohistochemical findings

Gross examination revealed a well-circumscribed but unencapsulated, whitish, multilobulated nodular mass measuring 6 cm in its greatest diameter (Fig. 4). The cut surface was whitish and firm in consistency with a whorled trabecular pattern (Fig. 4). Histologically, the tumor was composed predominantly of intersecting short fascicles of tightly packed, bland-looking spindle-shaped cells with a moderate amount of eosinophilic cytoplasm (Fig. 5A, B). Nuclei were elongated, sometimes with blunt

Discussion

A wide variety of mesenchymal tumor and tumor-like lesions may arise from the oral cavity at various ages (Table 1) [3]. Among these, SFT occurs rarely, accounting for 3% of all tumors arising in this site [1], [12], [14]. The most common regions involved by SFT are the cheek and the tongue [1], [11], [14], [17], [24]. These two sites are the most frequently traumatized areas within the mouth, so that some authors have postulated a potential traumatic pathogenesis for this tumor [1], [17].

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