Fibrosarcoma

Fig. 31.1

Fibrosarcoma. The tumor is composed of monomorphic elongated, spindle cells that grow in interlacing fascicles, forming a so-called herringbone pattern

Fig. 31.2

Fibrosarcoma. Herringbone pattern

Fig. 31.3

Fibrosarcoma. The cells have tapered, dark nuclei with variably prominent nucleoli and scanty cytoplasm. Mitotic figures are present

Fibrosarcoma occasionally shows limited expression of SMA, representing myofibroblastic differentiation. CD34-positive tumors with fibrosarcoma morphology probably represent fibrosarcoma arising in a dermatofibrosarcoma protuberans or fibrosarcoma-like progression in solitary fibrous tumor.

The congenital-infantile variant is usually more cellular and composed of smaller cells with prominent mitotic activity. Foci of necrosis may be present. Unlike the adult variant, the interlacing fascicular (herringbone) pattern is not always seen.

The tumor cells express vimentin, but not always desmin, S100 protein, or smooth muscle actin. Recently, a novel chromosomal translocation t(12;15)(p13;q25) has been identified in the congenital-infantile group, giving rise to an ETV6–NTRK3 fusion gene.

Differential Diagnosis

Fibrosarcoma is a diagnosis of exclusion, once the possibility of other spindle cells tumors such as low-grade fibromyxoid sarcoma (and its variants hyalinizing spindle cell tumor with giant rosettes), myxofibrosarcoma, dermatofibrosarcoma protuberans, desmoid tumor, synovial sarcoma, malignant peripheral nerve sheath tumor, spindle cell melanoma, and spindle cell squamous carcinoma have been ruled out.

Sclerosing epithelioid fibrosarcoma (SEF) and the inflammatory fibrosarcoma are distinct entities from fibrosarcoma. SEF is a low-grade sarcoma and is composed of small- to medium-sized epithelioid cells with a clear or pale cytoplasm, arranged in cords and strands, and embedded in a fibrotic and hyalinized stroma. A subset of SEF appears to be related to low-grade fibromyxoid sarcoma. Inflammatory fibrosarcoma is synonymous to inflammatory myofibroblastic tumor or acral myxoinflammatory fibroblastic sarcoma. Inflammatory fibrosarcoma is composed of fibroblastic and myofibroblastic spindle cells accompanied by an inflammatory infiltrate of plasma cells, lymphocytes, and/or eosinophils.

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