Monophasic Synovial Sarcoma of Tongue: A Rarest of Rare Case Scenario

Abstract

Synovial sarcoma is a rare tumour of head and neck. Primary synovial sarcoma of tongue is very uncommon. Based on morphology, it can be classified as classical biphasic variant, monophasic spindle cell variant, monophasic epithelial variant and poorly differentiated variant. The authors with an index case of 74 year old lady with monophasic spindle cell synovial sarcoma of oral tongue which is one of the rarest variants (our case is the 15th case reported of synovial sarcoma of the tongue and only the 3rd case in the world which had a monophasic histopathologic pattern) studied the morphology and described the disease entity in detail. She was treated with wide local excision of sarcoma followed by adjuvant radiotherapy.

Introduction

Synovial sarcoma (SS) is a type of malignant soft tissue tumour. The World Health Organisation (WHO) defines synovial sarcoma as ‘mesenchymal spindle cell tumours which display variable epithelial differentiation, including glandular formation and have a specific chromosomal translocation t(x:18) (p11;q11) [1].Most of these tumours occur in the lower extremities. Only 5–10% are found in the head and neck region [2] and its presence in the oral cavity is very rare. We hereby discuss synovial sarcoma of tongue with an index case of monophasic synovial sarcoma of tongue in a 74 year old lady.

Case Study

A 74 year old woman presented to the ENT department of our hospital with complaint of a progressively growing mass in the right lateral border of tongue associated with dysphagia for the last 3 months. Local ENT examination revealed a 5 × 2 cm ulceroproliferative growth over right lateral border of tongue extending from about 1 cm posterior to tip of tongue to 1 cm short of base of tongue and glossotonsillar sulcus on the right side (Fig. 1). It was hard on palpation, tender, but did not bleed on touch. Tongue movements were normal. There was no involvement of floor of mouth, alveolus, vallecula, epiglottis and tonsil. Cervical lymphadenopathy was absent. Multiple punch biopsies were taken under local anaesthesia and sent for histopathological examination which showed poorly differentiated sarcoma. MRI neck revealed 5 × 1 × 3 cm ulcerated mass involving right lateral border of tongue with infiltration of intrinsic muscles of tongue. PET CT revealed a FDG avid heterogenously enhancing ill defined mass with ulcerated contour and infiltrative margin involving right lateral border of tongue with infiltration of intrinsic muscles. Mandible was not involved. Mildly FDG avid subcentimetric cervical lymph nodes were seen at right level II and left level V. The patient underwent a wide local excision of the sarcoma with clear margins of at least 1 cm all around. She had an uneventful recovery. The surgical specimen which measured 6 × 4 × 2 cm was sent for histopathological examination. Multiple sections from the tongue revealed a malignant tumour composed of short, plump spindle cells occurring as intersecting fascicles and focal stroriform pattern. The cells had pleomorphic round to oval vesicular nuclei with prominent nucleoli and scant to moderate amount of cytoplasm. Occasional atypical mitotic figures were identified along with interspersed mild chronic inflammatory cell infiltrate and entrapped skeletal muscle fibres (Fig. 2). The margins were free of malignant cells all around the lesion. Immunohistochemistry profile was done for confirmation. The tumour cells were immunoreactive for BCL-2, Vimentin (Fig. 3) and CD 99 and negative for PAN CK, SMA, S 100 and CD 34. The diagnosis was confirmed as monophasic spindle cell synovial sarcoma with Grade 1, pT2aNx. The patient was subsequently sent for adjuvant radiotherapy following which the patient has been disease free (local/remote) during 02 years of follow up.

Fig. 1.

Ulceroproliferative growth over right lateral border of tongue

Fig. 2.

H and E section showing fascicular arrangement of spindle cells

Fig. 3.

Immunohistochemistry showing positivity for vimentin

Discussion

Synovial sarcoma is a rare tumour in the head and neck region. The most common site involved is lower limb (60–75%), followed by upper limb (15–20%) [3]. Synovial sarcoma of the head and neck account for just 6–7% of all cases [3], among which hypopharynx is the most common site reported [4].

The name ‘synovial sarcoma’ was coined early in the twentieth century, as some researchers thought of the microscopic similarity of some tumours to synovium, and its propensity to arise adjacent to joints, indicated a synovial origin, however, the actual cells from which the tumour develops are unknown and not necessarily synovial [5]. The patients are usually young adults between 15 and 40 years of age. Males are affected more often than females with a ratio of 1.2:1 [6]. However, our patient was a 74 year old female.

On microscopic examination, synovial sarcoma can have two cell types—fibrous (known as spindle or sarcomatous cell is relatively small and uniform and found in sheets) and epithelial. Classical synovial sarcoma has a biphasic appearance with both cell types. They can also appear to be of monophasic fibrous or monophasic epithelial type. A rare poorly differentiated type may also be present [5]. Hajdu et al. [7] proposed a unicellular theory of origin which suggested a common multipotential mesenchymal cell (fibroblast and/or histiocyte) that produces tumours. The common origin is supported by histologic, histochemical, cytologic, electron microscopic and tissue culture techniques, all of which demonstrate no basic difference between spindle cells and epithelial cells.

Most cases of synovial sarcoma are associated with reciprocal translocation t(x;18)(p11.2;q11.2). The diagnosis of synovial sarcoma is typically made based on histology and can be confirmed by the presence of t(X;18) [8]. This translocation event between the SS18 gene on chromosome 18 and one of 3 SSX genes (SSX1, SSX2 and SSX4) on chromosome X causes the presence of a SS18-SSX fusion gene. SS18-SSX is thought to underlie synovial sarcoma pathogenesis through dysregulation of gene expression [5].

Immunohistochemically, the synovial sarcoma tumour cells are strongly and uniformly positive for vimentin, with focal positivity for various cytokeratins and EMA (epithelial membrane antigens). Positive cytoplasmic BCL-2 staining in present in up to 93% of tumours, and almost 73% stain positively for CD99. In up to 21% of tumours, the S-100 protein may be focally expressed [9]. In our case, the tumour cells were immunoreactive for BCL-2, Vimentin and CD 99 and negative for PAN CK, SMA, CD 5, CD 3, CD 20, S 100 and CD 34 (Fig. 4).

Fig. 4.

Negative for CD5, CD3, CD20

Positive nuclear expression of TLE1 antibody occurs in about 90% of SS cases [10]. TLE1 is a transcriptional corepressor that binds to a number of transcription factors and plays an important role in the WNT/b-catenin signalling pathway, which is known to be associated with SS [11]. Occasionally, molecular confirmation of the SS associated fusion gene [t(X:18)(p11.2:q11.2)] by RT-PCR may be required [12].

Treatment of synovial sarcoma of head and neck region involves surgical excision with wide margins. The role of radiotherapy alone or as adjuvant is controversial. Keeping in view the old age of our patient along with the presence of occasional atypical mitotic figures the patient was advised to undergo postoperative radiotherapy.

de Almeida et al. [13] reported 12 cases of SS originating in the tongue, of which one was female. Agarwal et al. [14] reported a case of monophasic SS in the base of tongue in a 22 year old man. Villaroel-Salinas et al. [15] reported another case of SS of base of tongue in a 31 year old woman. Out of these only two cases were of the monophasic type, rest all had a biphasic pattern.

On extensive review of English literature, our case is the 15th case reported of synovial sarcoma of the tongue and only the third case which has a monophasic histopathologic pattern.