Adult Fibrosarcoma

Union for International Cancer Control (UICC) or American Joint Committee on Cancer (AJCC) staging would be appropriate.

Adult fibrosarcoma has been reported to show multiple numerical and structural chromosomal abnormalities, although older data should be interpreted with caution. A recent report of an STRN3-NTRK3 fusion in a strictly defined adult fibrosarcoma suggests a possible link to other NTRK-rearranged mesenchymal neoplasms.

Adult fibrosarcoma is a circumscribed, firm, white or tan mass. Hemorrhage and necrosis can be seen in high-grade tumors.

Adult fibrosarcoma is composed of relatively monomorphic spindle cells, showing no more than a moderate degree of pleomorphism. The tumor cells are characteristically arranged in long, sweeping fascicles that may be angled in a chevron-like or herringbone pattern. Storiform areas can be focally present. The cells have tapering hyperchromatic nuclei with variably prominent nucleoli and scant cytoplasm. Mitotic activity is almost always present but variable. The stroma has variable collagen, from a delicate intercellular network to paucicellular areas with diffuse or keloid-like sclerosis or hyalinization. Some adult fibrosarcomas may contain relatively bland zones mimicking fibromatosis. By immunohistochemistry, adult fibrosarcomas may occasionally show limited expression of SMA or calponin, representing focal myofibroblastic differentiation. CD34-positive tumors showing fibrosarcoma morphology typically represent fibrosarcomatous dermatofibrosarcoma protuberans or high-risk solitary fibrous tumors.

Not clinically relevant

More than 80% of strictly defined adult fibrosarcomas are high-grade, with an overall survival rate of < 70% at 2 years and < 55% at 5 years. These sarcomas metastasize to lungs and bone, especially the axial skeleton, and rarely to lymph nodes. It is likely that behavior is related to grade, tumor size, and depth, although data are limited. The probability of local recurrence relates to completeness of excision.

Not clinically relevant

Essential: relatively monomorphic spindle cells showing no more than moderate nuclear pleomorphism; fascicular, herringbone architecture with variable collagen production; an immunohistochemical and molecular genetic diagnosis of exclusion.