Pathology of Myxofibrosarcoma [Infographic]

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Pathology of Myxofibrosarcoma

Dr Sampurna Roy MD 2022

Myxofibrosarcoma, previously known as myxoid malignant fibrous histiocytoma, is considered one of the most common fibroblastic sarcomas of the elderly, predominantly affecting patients between sixty and eighty years of age.

It is a distinct entity that frequently arises in the skin.

The tumour usually presents as painless, slow growing, skin colored or erythematous nodules or tumours.

Most lesions are located in the lower limbs and rarely on the trunk, head and neck.

About two-thirds of the cases develop in the dermal and subcutaneous tissues, and one third in the fascia and skeletal muscle.

Macroscopically the tumour has a gelatinous appearance.

Microscopic features:

The tumours are classified as low, intermediate and high grade.

Low grade: Characterized by hypocellularity, cells with hyperchromatic and pleomorphic nuclei associated with extensive myxoid areas.

Intermediate grade tumors are more cellular with frequent nuclear atypia.

Finally, high-grade tumors are densely cellular, pleomorphic, with numerous mitotic figures, areas of hemorrhage and necrosis.

Few areas of myxoid stroma are found with a predominantly solid component.

A characteristic histological finding is the presence of elongated, curvilinear, thin-walled blood vessels.

It is important to note that skin biopsy, when taken superficially, may show misleading features, since the shallow portions of the tumor show benign characteristics, whereas deeper samples show histomorphological features of malignancy.

Therefore superficial biopsies may underclassify a high degree tumor or even classify it as a benign neoplasm.

This peculiar characteristic makes it very important to represent the lesion adequately for histopathological examination.

Due to the low specificity of immunohistochemistry in myxofibrosarcoma, the results should always be interpreted with caution.

The neoplastic cells are often positive for vimentin and CD34, and rarely positive for smooth muscle actin.

Desmin, cytokeratins, S100 and HMB-45 ; CD68 are usually negative.

Differential diagnosis-

-Intramuscular myxoma- no pleomorphism

-Superficial angiomyxoma- No pleomorphism

-Low grade fibromyxoid sarcoma (less vascular, less pleomorphic and less uniformly myxoid)

-Myxoid liposarcoma (lipoblasts and vessels with branching pattern present, less pleomorphic.)

- Myxoid Leiomyosarcoma

-Myxoid variants of nerve sheath tumour and smooth muscle tumour- (immunohistochemistry plays an important role in establishing the final diagnosis).

Visit: nerve sheath myxoma ; myxoid Neurofibroma; myxoid malignant peripheral nerve sheath tumour.

The final diagnosis of a myxofibrosarcoma is reached after examination of the clinical, radiologic, light microscopic, immunohistochemical and ultrastructural features of the lesion.

The electron microscopic demonstrate fibroblast-like cells, histiocyte-like cells, intermediate cells, primitive appearing cells, and vacuolated cells which help in establishing the diagnosis of the tumour.

"The well-characterized myxofibrosarcoma cell line MUG-Myx1 will be a useful tool to gain further insights into the pathogenesis of myxofibrosarcoma and explore new treatment options. Targeting stem-like cells with increased ALDH1 expression may especially facilitate the development of better treatment for patients suffering from myxofibrosarcomas."

Therapy consists of surgical resection with a safety margin of at least 2 cm.

High local recurrence rate (50-60%), regardless of the grade, results in the indication of adjuvant radiotherapy.

Metastasis occur in 20-35% of high and intermediate grade tumors, especially in bones and lungs.

As it is a rare disease, more studies are needed to establish the benefit of chemotherapy.

Myxofibrosarcoma: Pathology Infographic