Ossifying fibromyxoid tumour of soft parts (OFMT)

Definition

A rare tumour of soft tissue of unknown histogenesis with a lobular architecture, predominantly of epithelioid cytology, with cells arranged in cords or trabeculae, a myxocollagenous stroma and often peripheral metaplastic bone formation.   Incomplete Schwannian or cartilaginous differentiation have been proposed.  A risk stratification has been proposed into "typical", "atypical" and "malignant" tumours.  Childhood tumours, deep tumours and tumours with atypical features arguably have alternative diagnoses1.

Epidemiology

This is a rare tumour, with approximately 320 cases reported in the published literature. There is a mild male predominance5,6,7. Patients have a median age of 50 years and a range of 14 to 83 years5,6,7.

Clinical features

The tumour is most commonly located on the extremities, less commonly on the head and neck or trunk5. It presents as a slow growing painless mass, often present for years prior to surgery7.

Radiology

Radiology will commonly show the peripheral ossification.

Macroscopic appearances

The tumour is subcutaneous. It does not involve muscle except for superficial musculature if on the face. Rarely, there is extension into the dermis. It is circumscribed with a dense fibrous pseudocapsule, sometimes lobulated. It is firm, usually with a glistening cut surface.

Histopathology

It is composed of lobulated nests of small bland round cells within a stroma which varies from myxoid to hyaline. The lobules are separated by fibrous septa. Most, but not all, cases have a layer of bone spicules peripherally, which may be of variable extent6. (In one case, the bone was located centrally4.) The bone may incorporate fat but not haemopoietic tissue. The bone may be associated with a multinucleate giant cell component. There are often zones of hyalinisation. Some cases show necrosis.

The tumour cells form cords / trabeculae but not glands. The cells are predominantly epithelioid but may be focally spindled. Cytoplasm is pale to eosinophilic. Nuclei are fairly uniform with small central nucleoli. There may be occasional nuclear grooves or pseudo-inclusions. The mitotic count is variable, up to 40 / 50 HPF, without atypical mitoses.

Malignant ossifying fibromyxoid tumour has been defined as the presence of both areas of typical OFMT and areas showing a combination of high nuclear grade, high cellularity and mitotic activity above 2/50 HPF5,6.  Malignant tumours may also show necrosis and infiltrative growth. In one study, these features were present in 15 of 46 cases5.

Immunohistochemistry

Ultrastructure

Cells show external lamella2. There are primitive intercellular junctions2.

Gene expression

FISH studies have shown hemizygous deletions for INI-1 and PANX2 with hemizygosity of 22q5.

Differential diagnosis

• Cutaneous mixed tumours

• Low-grade fibromyxoid sarcoma: the cells are predominantly spindled, forming whorled or storiform patterns; there ay be hyaline rosettes: S-100 is negative: there is a t(7;16) translocation3.

• Extra-skeletal osteosarcoma

• Epithelioid smooth muscle tumour

• Epithelioid Schwannoma

• Glomus tumour

• Chondroid syringoma

• Soft tissue aneurysmal bone cyst

• Sclerosing epithelioid fibrosarcoma

• Chondromyxoid tumours arising from nasal cartilage

• Myxoid chondrosarcoma

• Reticular perineuroma

• Primary bone tumours

Management

Complete local excision with a margin.

Prognosis

About 20% of cases recur, often after an interval of years. A mitotic rate of greater than 2 / 50 HPF predicts local recurrence. Some claim that if strict diagnostic criteria are applied, the tumour does not metastasis1: other authors have reported atypical cases as developing distant metastases.  In one study in which 15 of 46 cases were classified as malignant, of the 9 with follow up, 2 patients developed local recurrences and 3 developed distant metastases and died from disease5.

References

0 Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, pages 77

1 Miettinen M, Finnell V,Fetsch JF. Ossifying fibromyxoid tumor of soft parts--a clinicopathologic and immunohistochemical study of 104 cases with long-term follow-up and a critical review of the literature. Am J Surg Pathol 2008; 32:996-1005

2 Min KW, Seo IS,Pitha J. Ossifying fibromyxoid tumor: modified myoepithelial cell tumor? Report of three cases with immunohistochemical and electron microscopic studies. Ultrastruct Pathol 2005; 29:535-48

3 Reid R, de Silva MV, Paterson L, et al. Low-grade fibromyxoid sarcoma and hyalinizing spindle cell tumor with giant rosettes share a common t(7;16)(q34;p11) translocation. Am J Surg Pathol 2003; 27:1229-36

4 Holck S, Pedersen JG, Ackermann T, et al. Ossifying fibromyxoid tumour of soft parts, with focus on unusual clinicopathological features. Histopathology 2003; 42:599-604

5 Graham RP, Dry S, Li X, Binder S, Bahrami A, Raimondi SC, et al. Ossifying fibromyxoid tumor of soft parts: a clinicopathologic, proteomic, and genomic study. Am J Surg Pathol. 2011 Nov;35(11):1615-25.

6 Folpe AL, Weiss SW. Ossifying fibromyxoid tumor of soft parts: a clinicopathologic study of 70 cases with emphasis on atypical and malignant variants. Am J Surg Pathol. 2003 Apr;27(4):421-31.

7 Enzinger FM, Weiss SW, Liang CY. Ossifying fibromyxoid tumor of soft parts. A clinicopathological analysis of 59 cases. Am J Surg Pathol. 1989 Oct;13(10):817-27.

This page last revised 19.10.2011.

©SMUHT/PW Bishop