Pathology of Sclerosing Epithelioid Fibrosarcoma

Dr Sampurna Roy MD                

Sclerosing epithelioid fibrosarcoma is a rare variant of fibrosarcoma, originally described in 1995 by Meis-Kindblom et al.

The tumour occurs in young and middle aged adults.

Most examples arise in the deep skeletal muscles of adults.

In rare cases the tumour may arise along the neuraxis.

These tumours may demonstrate aggressive clinical behavior, compared to those arising in the more typical location of deep skeletal muscles.  

Sclerosing epithelioid fibrosarcoma can also occur as a primary tumour in the bone.

Common sites include lower limb, limb girdle, head and neck region, back or chest wall.

Despite the relatively bland appearance and low mitotic activity, the tumour is capable of local recurrence and distant metastasis often several years after surgical removal.

Macroscopically, the tumours are usually less than 10 cm in diameter and presents as well circumscribed, lobulated masses.

Microscopic features:

Histologically, the tumour is hypocellular with prominent areas of stromal hyalinization.

The hyaline stroma may be mistaken for osteoid.

The cellular areas are characterized by small to medium-sized round to ovoid, relatively uniform, bland cells, often with clear cytoplasm, arranged in cords and strands, embedded in the hyalinized fibrous stroma.

In some areas, nests, sheets, acini or alveolar structures are also noted.

The mitotic count is usually less than 1 per 10 high power fields.

In some cases the tumour may exhibit large areas of necrosis together with areas of high grade nuclear anaplasia and active mitosis.

Immunohistochemistry:  

Vimentin - Diffuse and strong positivity.

Epithelial membrane antigen (EMA) - Focal or weak positivity.

Tumour cells are negative for CAM5.2 , AE1/AE3, S100 protein, HMB45, desmin,  alpha-smooth muscle actin, CD34 and LCA.

Differential diagnosis : 

Metastatic carcinoma ;  Hyalinised leiomyoma ; Sclerosing lymphoma ; Fibromatosis ; Nodular fasciitis;  Benign fibrous histiocytomas ; Ossifying fibromyxoid tumours  ; Clear cell sarcomas ; Epithelioid sarcomas;  Synovial sarcomas ;  Extraskeletal osteosarcomas ; Extra-skeletal myxoid chondrosarcoma.