Low-grade myofibroblastic sarcoma of the mandible: A rare tumour of childhood :[PAUTHORS], Journal of Oral and Maxillofacial Pathology (JOMFP)

CASE REPORT
Year : 2023 | Volume : 27 | Issue : 5 | Page : 10--14

Low-grade myofibroblastic sarcoma of the mandible: A rare tumour of childhood

Saikat Mitra¹, Satnam S Jolly², Anindita Sinha³, Debajyoti Chatterjee¹,
¹ Department of Histopathology, Postgraduate Institute of Medical Education and Research, Chandigarh, India
² Department of Oral and Maxillofacial Surgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India
³ Department of Radiodiagnosis, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Correspondence Address:
Debajyoti Chatterjee
Department of Histopathology, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
India

Abstract

Low-grade myofibroblastic sarcoma is a rare and indolent tumour of soft tissue. This tumour is relatively common in the head and neck region followed by extremities. Primary low-grade myofibroblastic sarcoma of the mandible is very rarely reported and the occurrence of this tumour in a child is very unusual. A 7-year-old male child presented with a swelling in right angle of mandible. X-ray and computed tomography scan showed a lytic lesion. The lesion was excised and the tissue was sent for histopathological evaluation, which revealed a cellular spindle cell neoplasm arranged in fascicles. The tumour was partly circumscribed and lobulated. On immunohistochemistry (IHC), these tumour cells showed cytoplasmic positivity for vimentin, and smooth muscle actin showed 'tram-track' pattern of positivity. The case was diagnosed as low-grade myofibroblastic sarcoma. There are no definite clinical features or pathognomonic radiological appearances of this tumour that can differentiate this rare tumour from other commonly encountered gnathic bone tumours, such as osteosarcoma, inflammatory myofibroblastic tumour, etc., Histopathological diagnosis coupled with ancillary investigations such as IHC is important to establish a definite diagnosis and rule out the differentials. The exact biological behaviour of this tumour is not known.

How to cite this article:
Mitra S, Jolly SS, Sinha A, Chatterjee D. Low-grade myofibroblastic sarcoma of the mandible: A rare tumour of childhood.J Oral Maxillofac Pathol 2023;27:10-14

How to cite this URL:
Mitra S, Jolly SS, Sinha A, Chatterjee D. Low-grade myofibroblastic sarcoma of the mandible: A rare tumour of childhood. J Oral Maxillofac Pathol [serial online] 2023 [cited 2023 Mar 21 ];27:10-14
Available from: https://www.jomfp.in/text.asp?2023/27/5/10/369171

Full Text

Introduction

Myofibroblasts, which first described by Gabbiani et al.[1] in 1971 and have an important role in wound contracture and healing. Subsequently, several authors described the histomorphology, immunohistochemistry (IHC), and ultrastructure of myofibroblasts in detail. Myofibroblasts can be defined as modified fibroblasts with smooth-muscle-like features.[2] Low-grade myofibroblastic sarcoma is a rare soft tissue tumour that has been described in various organ systems, most commonly in the head and neck region, and has its origin in the myofibroblasts.[3] Because of its rarity, the exact biology of this tumour, its treatment protocol, and prognosis are still not well established. Low-grade myofibroblastic sarcoma of bone has been rarely described.[4] Here, we report a case of low-grade myofibroblastic sarcoma of the mandible in a child.

Clinical and radiological features

A 7-year-old boy presented with a history of swelling over the right angle of the mandible for one and half months. The swelling was painless, gradually progressive in nature, and it was not associated with any other symptoms. The patient did not have any history of prior trauma or infection in the oral cavity or an impacted tooth. There was no contributory past or family history.

Initial radiology workup, including X-ray and computed tomography (CT) scan, revealed an expansile lytic lesion in the right angle of the mandible. There was an evidence of cortical breach. Matrix mineralisation was absent. There was a loss of fat plane with the adjacent masseter [Figure 1]. Few submandibular lymph nodes were identified on ultrasonography, which appeared reactive in nature.{Figure 1}

The patient was taken up for surgery. A segment of the mandible containing the tumour, measuring 3 × 2.5 × 1.5 cm, was removed along with one tooth under general anaesthesia. The postoperative course was uneventful.

Pathological Examination

On gross examination, a tumour was identified within the mandible measuring 2 × 1.5 × 1.5 cm. It was partly circumscribed; the cut surface was whitish, homogeneous, and firm. The tumour was involving the mandible and also focally pushed the surrounding soft tissue. No gross haemorrhage or necrosis was noted.

Microscopic examination from different areas of the tumour revealed a vague nodular architecture [Figure 2]a. The tumour was cellular and was composed of intersecting fascicles of spindle cells [Figure 2]b. Few areas showed sheet-like architecture. The tumour cells were dispersed on a fibrocollagenous matrix and showed myxoid degeneration at places. Individual tumour cells showed moderate nuclear pleomorphism and had fusiform to spindled nuclei, coarse chromatin, occasional conspicuous nucleoli, and moderate cytoplasm [Figure 2]c. Few thin-walled blood vessels were noted. A small focus of ischemic necrosis was noted. Mitosis was variable, ranging from 0–1/10 to ~5–6/10 HPF at places. The underlying stroma also showed many infiltrating mature lymphocytes and plasma cells. However, even on extensive sampling, no malignant osteoid was identified anywhere in the lesion. The tumour was breaching the bony cortex with the formation of reactive, new woven bone. The tumour was seen abutting the adjacent soft tissue and skeletal muscle bundle, however, not infiltrating them. The resection margins were free of tumour. The tumour was graded as per Fédération Nationale des Centres de Lutte contre le Cancer (FNCLCC)criteria into grade 1 (score 3).{Figure 2}

On IHC, the tumour cells were diffusely positive for vimentin and smooth muscle actin (SMA) [Figure 2]d. The staining pattern of SMA had a typical 'tram-track' appearance [Figure 2]e. The tumour cells were negative for immunohistochemical markers H-caldesmon, desmin, myogenin, S100, STAT-6, TLE-1, pan-cytokeratin, epithelial membrane antigen, and MUC-4 IHC. H3K27me3 and INI-1 showed retained nuclear expression. Anaplastic lymphoma kinase (ALK) IHC (ALK-1 and D5F3 clone) was also negative. Ki67 labelling index was variable, reaching up to ~10–12% at some foci [Figure 2]f. SATB-2 IHC was also performed, and it showed weak nuclear immunostain in tumour cells. However, no malignant osteoid was identified even on extensive sampling; hence, the possibility of low-grade osteosarcoma was ruled out.

Diagnosis

Based on the histological and immunohistochemical features, a final diagnosis of low-grade myofibroblastic sarcoma was provided.

Follow-up

The child was kept on close follow-up. No further adjuvant therapy was provided. A magnetic resonance imaging was done 1 year after the surgery and showed no evidence of residual or recurrent lesion. The patient was asymptomatic 18 months after surgery and is on regular follow-up.

Discussion

The first series of low-grade myofibroblastic sarcoma was described by Mentzel et al.[3] in 1998, where the authors studied 18 such cases. The authors noted a wide age range of clinical presentations. The tumour most commonly involved the oral cavity and had an infiltrative border. This tumour type was recognized by WHO in its 2002 edition of soft tissue and bone tumour classification.[5]

Low-grade myofibroblastic sarcoma is a rare tumour and occurs predominantly in adult patients with a slight male preponderance. The most common site of involvement is the head and neck, especially the oral cavity and tongue followed by extremities.[6],[7],[8] Rarely, unusual sites of involvement including breast and retroperitoneal soft tissue have been reported.[9] Children are rarely affected and very rare cases in infants have also been reported.[10]

A recent literature review by Jayasooriya et al.[11] described 33 cases of low-grade myofibroblastic sarcoma that purely involved the oral cavity. The patients had an age range of 7–74 years with a bimodal age distribution. Eight of these cases arose exclusively from the mandible. The demography and site of lesion in the index case corroborate with the published literature.

The scarcity of imaging studies of low-grade myofibroblastic sarcoma makes imaging characteristics of this disease still poorly understood. One case of distal femur tumour presented with an extensive multi-cystic lesion invading the cortical bone and surrounding soft tissue. Few cases showed permeant tumour tissues and osteolytic bone destruction. X-ray or CT scan of two low-grade myofibroblastic sarcoma cases revealed significant ossification masses within bones. Low-grade myofibroblastic sarcoma ossification is presumably attributed to multiple differentiations of intratumoural myofibroblasts into metaplasia-induced osteoblasts.[12] The imaging features are often non-specific and overlap with other lesions, including osteosarcoma, fibrosarcoma, and inflammatory myofibroblastictumour.

A definitive diagnosis of low-grade myofibroblastic sarcoma needs histopathological examination along with ancillary techniques, such as IHC and ultrastructural evaluation. Histology of low-grade myofibroblastic sarcoma reveals a locally invasive tumour, composed of fascicles of spindle-shaped cells. Commonly, the tumour cells are arranged in a storiform or herringbone pattern. Individual tumour cells have ill-defined palely eosinophilic cytoplasm and fusiform hyperchromatic nuclei that are either elongated and wavy or plump with small nucleoli and that usually present with mild nuclear pleomorphism and a low mitotic rate (1–6 per 10 HPFs).[3] Immunohistochemically, all myofibroblasts are stained positive for vimentin, and most of low-grade myofibroblastic sarcoma show immuno reactivity for at least 1 myogenic marker, including SMA, calponin, and muscle-specific actin. The immunohistochemical staining of SMA shows a characteristic 'tram-track' appearance, where the periphery of the cytoplasm in the tumour cells shows immune staining, instead of uniform cytoplasmic staining observed in smooth muscle cells. In addition, some cases have been positive for calponin and CD34, and all cases have been negative for S100 protein and epithelial markers.[13]

The differential diagnosis of low-grade myofibroblastic sarcoma includes a number of benign and malignant spindle cell neoplasms. Desmoplastic fibroblastoma (collagenous fibroma) arises frequently in male patients and represents a rather well-circumscribed neoplasm composed of cytologically bland spindled to stellate 'reactive-appearing' fibroblasts without increased proliferative activity set in a fibromyxoid or densely fibrous matrix.[14] Tumour cells in desmoplastic fibroblastoma stain only infrequently and focally for actin and are negative for desmin. The rare fibrosarcoma in children and adults may also resemble low-grade myofibroblastic sarcoma. Fibroblastic tumour cells in fibrosarcoma, however, have less eosinophilic cytoplasm and lack immunohistochemical and ultrastructural features of myofibroblasts. Low-grade malignant peripheral nerve sheath tumours are composed of tumour cells with elongated and wavy nuclei that contain evenly distributed chromatin, and often perivascular whorling is noted. In addition, at least 50% of cases of malignant peripheral nerve sheath tumour stain focally for S-100 protein but lack positivity for myogenic markers. Loss of H3k27me3 has been found to be a sensitive diagnostic marker in malignant peripheral nerve sheath tumours.[15] Low-grade leiomyosarcoma shows mainly pushing margins and is composed of well-developed fascicles of spindled tumour cells containing a more eosinophilic, often fibrillary cytoplasm and cigar-shaped nuclei with frequent paranuclear vacuolation. Immunohistochemical markers of smooth muscle differentiation, viz, H-caldesmon and desmin should be positive in leiomyosarcoma. Lack of neoplastic osteoid formation denies the possibility of low-grade central osteosarcoma. Inflammatory myofibroblastic tumour can show many morphological and immunohistochemical overlaps with low-grade myofibroblastic sarcoma. The inflammatory myofibroblastic tumour is characterised by a broad morphologic spectrum and usually exhibits inhomogeneous features of cytomorphology, architecture, and immunochemistry. In contrast, low-grade myofibroblastic sarcoma tends to be more uniform in appearance with higher cellularity, nuclear pleomorphism, and hyperchromasia. Low-grade myofibroblastic sarcoma shows a more widely infiltrating growth pattern than inflammatory myofibroblastic tumour. The inflammatory infiltrate in inflammatory myofibroblastic tumour is denser; however, low-grade myofibroblastic sarcoma can also show focal mild lymphocytic infiltrate. Immunohistochemical stains for myofibroblast-associated markers are not particularly useful in making the distinction between inflammatory myofibroblastic tumour and low-grade myofibroblastic sarcoma. ALK and cytokeratin expression is more commonly seen in inflammatory myofibroblastic tumour. Low-grade myofibroblastic sarcoma lacks the ALK-gene rearrangement, which is characteristically noted in inflammatory myofibroblastic tumour and can be detected by fluorescent in situ hybridisation.[16] All the above-mentioned differentials were considered in our case and an appropriate panel of IHC was also performed to rule out the possibilities.

Surgical resection with the aim of achieving clear margins is the current gold standard management for low-grade myofibroblastic sarcoma.[7] Xu et al.[17] on the basis of follow-up data on 96 patients concluded that surgical resection is the most effective therapy for low-grade myofibroblastic sarcoma. In addition, the authors mentioned that chemotherapy and/or radiation therapy should not be routinely performed in low-grade myofibroblastic sarcoma, especially for those with negative margins after surgery.

Yamada et al.[18] conducted a literature review on 38 cases of oro-maxillofacial low-grade myofibroblastic sarcoma and found the recurrence rate to be 38.2%, whereas the tumour located in the mandible has the second highest recurrence rate. The tumour size was the most important contributing factor affecting recurrence in their study. In a recent study by Kim et al.[19] a univariate analysis of 15 cases of low-grade myofibroblastic sarcoma identified tumour size, a positive or close resection margin, and local infiltration into the surrounding tissue to be independent risk factors for recurrence. No definite parameters of histopathology or IHC have been identified as risk factors for recurrence in such tumours. Our index case also did not receive any adjuvant therapy and remains disease free 18 months postsurgery.

Conclusion

Low-grade myofibroblastic sarcoma is an unusual osseous neoplasm. It needs to be differentiated from other spindle cell tumours of the bone using immunohistochemical expression pattern and/or electron microscopy. A close radiological and pathological correlation is mandatory to exclude other entities and to make an accurate diagnosis. The biologic behaviour of this rare neoplasm is difficult to predict because only a few cases have been reported so far in the bone. Reports of more cases in the literature would help in better management of this disease.

Declaration of patient consent

Written informed consent was obtained from the father of the patient.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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