- Definition: Malignant tumor of fibroblasts. Primarily affects deep soft tissues (thigh) or bone (knee).
- Patient Profile: Adults, ages 35-55.
- Presentation: Slowly enlarging, painless mass. Bony lesions can cause pain or pathologic fractures.
- Histology:
- Spindle-shaped cells arranged in a “herringbone” pattern.
- Diagnosis of exclusion (negative for S100, cytokeratin, etc.).
- Treatment: Wide surgical excision. Adjuvant radiation is common.
- Metastasis: Hematogenous spread, primarily to the lungs.
- Infantile Fibrosarcoma:
- Distinct entity in infants (<1 year old).
- Associated with t(12;15) ETV6-NTRK3 fusion gene.
- Excellent prognosis; responds well to NTRK inhibitors (e.g., larotrectinib).