Fibrosarcomas

Fibrosarcoma is a malignant soft tissue sarcoma arising from fibroblasts, characterized by a proliferation of spindle-shaped cells that produce collagen. It is relatively rare, representing a minority of soft tissue sarcomas, and can occur at any age. A distinct pediatric subset, infantile fibrosarcoma, occurs in early life and has its own clinical and molecular features.

Infantile fibrosarcoma is commonly associated with the ETV6-NTRK3 gene fusion, produced by a t(12;15) translocation. These tumors often present in infancy and can grow rapidly. Despite aggressive growth, they frequently respond well to surgical resection and, if needed, chemotherapy. Adult fibrosarcoma typically lacks a single defining genetic driver and most often presents as a deep, slow-growing mass in the extremities or trunk. Prognosis in adults depends on tumor size, depth, grade, and completeness of excision.

Histologically, fibrosarcoma shows malignant spindle cells arranged in a characteristic herringbone pattern, with varying cellularity, mitotic activity, and collagen production. Immunohistochemistry is generally non-specific; tumor cells are usually positive for vimentin and negative for markers of other lineages (such as keratin, S-100, desmin), but results can be variable. Diagnosis relies on biopsy with imaging to assess extent and, in suspected infantile cases, molecular testing for ETV6-NTRK3.

Management is multidisciplinary and centers on wide surgical excision with negative margins. Radiotherapy or chemotherapy is considered for unresectable tumors, positive margins, or high-risk cases. In tumors with NTRK fusions, targeted NTRK inhibitors may be effective, particularly for unresectable or metastatic disease.

Prognosis varies with age, tumor location and size, histologic grade, and surgical success. Infantile fibrosarcoma generally has a favorable outcome with appropriate therapy, while adult fibrosarcoma carries a higher risk of local recurrence and metastasis. Follow-up focuses on local control and surveillance for distant spread.