sarcoma

Sarcomas are malignant neoplasms derived from mesenchymal stem cells, in contrast to carcinomas which arise from epithelial cells. They are classified by tissue of origin: osteosarcoma (bone), chondrosarcoma (cartilage), liposarcoma (fat), rhabdomyosarcoma (skeletal muscle), leiomyosarcoma (smooth muscle), angiosarcoma (blood vessels), fibrosarcoma (fibrous tissue), and synovial sarcoma, among others. Sarcomas are relatively rare compared to carcinomas but are important in pediatric and young adult oncology (e.g., osteosarcoma, Ewing sarcoma, rhabdomyosarcoma are common in children/adolescents).

Key pathophysiology: Many sarcomas arise from genetic mutations or translocations—e.g., EWSR1-FLI1 translocation in Ewing sarcoma, RB1 and TP53 mutations in osteosarcoma (associated with Li-Fraumeni syndrome and hereditary retinoblastoma), and MDM2 amplification in well-differentiated liposarcoma. Radiation exposure and chronic lymphedema (Stewart-Treves syndrome, associated with angiosarcoma) are known risk factors.

Clinical significance: Sarcomas typically present as a painless, enlarging soft tissue mass or, in bone sarcomas, as pain with a mass and characteristic imaging findings (e.g., "onion-skin" periosteal reaction in Ewing sarcoma, "sunburst" pattern in osteosarcoma, "soap bubble" appearance in giant cell tumor of bone—though this is benign). Diagnosis requires biopsy with histopathology; immunohistochemistry (e.g., vimentin positivity, desmin for muscle origin) helps confirm mesenchymal origin and specific subtype.

Unlike carcinomas, which spread primarily via lymphatics, sarcomas metastasize hematogenously, most commonly to the lungs. Treatment often involves wide surgical excision, with chemotherapy and/or radiation depending on subtype and stage. Prognosis varies widely by sarcoma type, grade, size, and location.

High-yield boards associations: Osteosarcoma - knee region in adolescents, elevated ALP; Ewing sarcoma - diaphysis of long bones, EWSR1-FLI1 fusion, "small round blue cells"; Rhabdomyosarcoma - most common soft tissue sarcoma in children, desmin/myogenin positive; Kaposi sarcoma - HHV-8 associated, seen in HIV/AIDS patients, endothelial origin; Angiosarcoma - liver (associated with vinyl chloride, arsenic exposure), Stewart-Treves syndrome.