Pathology of Low-Grade Fibromyxoid Sarcoma ;
Pathology of Hyalinizing Spindle Cell Tumour with Giant Rosettes
Pathology of Low-Grade Fibromyxoid Sarcoma:
Low-grade fibromyxoid sarcoma was first described by Evans in 1987.Low-grade fibromyxoid sarcoma. A report of two metastasizing neoplasms having a deceptively benign appearance.
This is an aggressive tumour and local recurrences have been reported in approximately 10% of the cases, and distant spreading occurs in 5-10% of the cases.
Distant metastasis occurs mostly to the lungs.
Age: The tumour occurs in the third and fifth decade of life. (Average: 35 years)
Site: This is a neoplasm of the deep and subcutaneous soft tissue and are commonly located in the lower extremities.
Other sites include neck, axilla, chest wall, shoulder, buttock and the inguinal region.
The tumour may be rarely located in the mediastinum, retroperitoneum, mesentery and the pelvis.
Gross features: The tumours are round to oval shaped and well circumscribed with thin pseudocapsule.
The cut surface is homogenous with a firm and fibrous consistency.
Lee EJ, Hwang HJ, Byeon HK, Park HS, Choi H-S. A low grade fibromyxoid sarcoma originating from the masseter muscle: a case report. Journal of Medical Case Reports. 2015;9:176. doi:10.1186/s13256-015-0658-9.
The tumour consists of bland uniform fibroblasts arranged in a swirling, whorled growth pattern.
The cells are small, spindle to stellate shaped with poorly defined, palely eosinophilic cytoplasm and hyperchromatic ovoid nuclei.
These cells are embedded in a dense collagenous or myxoid stroma.
Cellularity is low to moderate and mitotic figures are rare. The recurrent tumours are usually more cellular.
The hyalinizing spindle cell tumour with giant rosettes is thought to be a closely related tumour differing only by the presence of collagen rosettes.
Immunohistochemistry: The tumour cells are strongly positive for vimentin.
There may be focal immunopositivity for actin, desmin & cytokeratin. CD34 and S100 protein are usually negative.
Low-grade fibromyxoid sarcoma is characterized by a recurrent balanced translocation t (7 ; 16) (q34; p11) resulting in an FUS-CREB3L2 fusion gene.
This same translocation is identified in cases of hyalinizing spindle cell tumor with giant rosettes, suggesting a pathogenetic link between these two entities.
Differential diagnosis :
Low- grade myxofibrosarcoma is characterized by the presence of prominent elongated, curvilinear capillaries and pseudolipoblasts, accompanied by an abundant myxoid matrix.
It has no extensive solid areas.
Low-grade fibromyxoid sarcoma is composed of bland spindle cells arranged in a whorled pattern with alternating myxoid and fibrous stroma.
Curvilinear capillaries are not prominent and cytological atypia is absent.
Hyalinizing Spindle Cell Tumour with Giant Rosettes:
This tumour was first reported by Lane et al in 1997. Hyalinizing spindle cell tumor with giant rosettes: a distinctive tumor closely resembling low-grade fibromyxoid sarcoma.Am J Surg Pathol. 1997 Dec;21(12):1481-8.
It is now regarded as a variant of low-grade fibromyxoid sarcoma.
It is a rare low-grade sarcoma with indolent behavior, and wide resection of the tumour with prolonged follow-up are needed because patients may develop late metastases.
Age: This painless, slow growing tumour can develop at any age.
It commonly occurs in young and middle aged adults (average age 38 years).
Site: The lesion is commonly located in the deep soft tissue of the extremities, particularly the thigh. Other sites include the chest wall, axilla, buttock and the neck.
Gross features: These are deep seated, oval, multilobulated , well circumscribed, pale, firm tumours.
The lesion usually ranges from 5-10 cm in maximal dimension.
Focal pseudocystic degeneration may be present.
The tumour consists of uniform oval to spindle cells with fibroblastic or neural-like appearance.
These are arranged in fascicles in a collagenous or myxoid stroma.
The most striking feature is the presence of hyalinized nodules surrounded by round or ovoid tumour cells giving the appearance of rosette or palisaded granuloma.
The eosinophilic area at the centre of the rosettes is composed of collagen fibrils.
Pleomorphism is minimal. Mitoses are scarce.
In small number of cases there may be hypercellular areas with cells showing nuclear enlargement and hyperchromatism.
The miototic activity may range from 1 to 20 per 10 high-power fields.
Immunohistochemistry: Spindle cells are immunoreactive for vimentin, HAM56, factor XIIIa , collagen IV, and CD68.
The rounded cells comprising the collagen rosettes are positive for vimentin, S100 protein, Leu7(CD57) , synaptophysin, protein gene product (PGP) 9.5 , neuron specific enolase and sometimes CD34.
The cells are negative for desmin, alpha-smooth muscle actin , keratin, and epithelial membrane antigen.
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