Version June 2024
| Tumor differentiation | |
| Tumor differentiation is histology specific and is generally scored as follows: | |
| Differentiation score | Definition |
| 1 | Sarcomas closely resembling normal adult mesenchymal tissue (eg, low-grade leiomyosarcoma) |
| 2 | Sarcomas for which histologic typing is certain (eg, myxoid/round cell liposarcoma) |
| 3 | Embryonal and undifferentiated sarcomas, sarcomas of doubtful type, synovial sarcomas, soft tissue osteosarcoma, Ewing sarcoma/primitive neuroectodermal tumor (PNET) of soft tissue |
| Histology-specific tumor differentiation score | |
| Histologic type | Score |
| Atypical lipomatous tumor/well-differentiated liposarcoma | 1 |
| Myxoid liposarcoma | 2 |
| Round cell liposarcoma | 3 |
| Pleomorphic liposarcoma | 3 |
| Dedifferentiated liposarcoma | 3 |
| Fibrosarcoma | 2 |
| Myxofibrosarcoma | 2 |
| Undifferentiated pleomorphic sarcoma (formerly termed malignant fibrous histiocytoma, pleomorphic type) | 3 |
| Well-differentiated leiomyosarcoma | 1 |
| Conventional leiomyosarcoma | 2 |
| Poorly differentiated/pleomorphic/epithelioid leiomyosarcoma | 3 |
| Biphasic/monophasic synovial sarcoma | 3 |
| Poorly differentiated synovial sarcoma | 3 |
| Pleomorphic rhabdomyosarcoma | 3 |
| Mesenchymal chondrosarcoma | 3 |
| Extraskeletal osteosarcoma | 3 |
| Ewing sarcoma/PNET | 3 |
| Malignant rhabdoid tumor | 3 |
| Undifferentiated sarcoma, not otherwise specified | 3 |
| NOTE: Grading of gastrointestinal stromal tumor, malignant peripheral nerve sheath tumor, embryonal and alveolar rhabdomyosarcoma and angiosarcoma (rapid growth, dissemination common), as well as extraskeletal myxoid chondrosarcoma, alveolar soft part sarcoma, clear cell sarcoma, and epithelioid sarcoma (slower growth, dissemination common) is not recommended under this system. The case for grading malignant peripheral nerve sheath tumor is debated. Although all these histologies have a high rate of dissemination, survival with metastatic disease varies widely. | |
| Mitotic count | |
| In the most mitotically active area of the sarcoma, 10 successive high-power fields (HPF; one HPF at 400x magnification = 0.1734 mm2) are assessed using a 40x objective. | |
| Mitotic count score | Definition |
| 1 | 0 to 9 mitoses per 10 HPF |
| 2 | 10 to 19 mitoses per 10 HPF |
| 3 | ≥20 mitoses per 10 HPF |
| Tumor necrosis | |
| Evaluated on gross examination and validated with histologic sections. | |
| Necrosis score | Definition |
| 0 | No necrosis |
| 1 | <50% tumor necrosis |
| 2 | ≥50% tumor necrosis |
| FNCLCC histologic grade | |
| G | G definition |
| GX | Grade cannot be assessed |
| G1 | Total differentiation, mitotic count and necrosis score of 2 or 3 |
| G2 | Total differentiation, mitotic count and necrosis score of 4 or 5 |
| G3 | Total differentiation, mitotic count and necrosis score of 6, 7, or 8 |
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