Soft tissue lesions
Soft tissue lesions strike fear in many pathologists as they are uncommon and may be difficult to diagnose. Malignant soft tissue lesions, i.e. cancerous soft tissue lesions, are usually sarcomas. Sarcomas are malignancies derived from mesenchymal tissue.
WHO classification of soft tissue lesions/tumours
- Adipocytic tumours.
- Fibroblastic/myofibroblastic tumours.
- "Fibrohistiocytic" tumours.
- Smooth muscle tumours.
- Skeletal muscle tumours.
- Vascular tumours.
- Perivascular (pericytic) tumours.
- Chondro-osseous tumours.
- Tumours of uncertain differentiation.
Biologic potential grouping
- Intermediate (locally aggressive).
- Intermediate (rarely metastasizing).
- All sarcomas are rare buggers.
- As the classification has been changing over the past years (with more subtypes being recognized/identified) numbers are variable from study-to-study.
- Once upon a time almost everything was called malignant fibrous histiocytoma; thus, it is listed as a common entity in some publications.
- Molecular testing plays an important role in soft tissue pathology.
- It is generally seen as an adjunct test that:
- Often is used to confirm the histomorphologic impression/quality control.
- Frequently has some prognostic significance.
- May directly affect treatment.
- Many tumours in soft tissue pathology are diagnosed inconjunction with the finding of chromosomal translocations.
|Storiform, AKA patternless pattern||whorled, cartwheel-like arrangement||pleomorphic undifferentiated sarcoma, solitary fibrous tumour, dermatofibrosarcoma protuberans, dermatofibroma|
|Herring bone||like herring bone (technique) for climbing a hill in cross country skiing; books on a shelf, where they have partially fallen over -- on the one shelf to the left and the one below to the right||fibrosarcoma, synovial sarcoma, MPNST|
|Fascicular||the long axis of the (spindle) cells are perpendicular to one another in adjacent bundles of cells||leiomyoma, leiomyosarcoma|
|Biphasic||nests of cells and stroma||synovial sarcoma, DSRCT, alveolar RMS|
- Memory device: herring bone DDx MSF = MPNST, Synovial sarcoma, Fibrosarcoma.
- Several systems exist.
- The US-CAP advocates the use of the French system over the NCI system.
- The French system is a better predictor metastases and mortality.
- Formally known as the grading system from the French Federation of Cancer Centres Sarcoma Group (FNCLCC).
- Differentiation (score 1-3).
- De facto, this is mostly the histologic type.
- Mitotic rate (score 1-3).
- Necrosis (score 0-2)
Obtaining a score:
- Add all the points from the three components.
- Grade 1 = 2-3.
- Grade 2 = 4-5.
- Grade 3 = 6-8.
- Standardized for histologic types.
- Most tumours = 3/3.
- Well-differentiated liposarcoma = 1.
- Myxoid liposarcoma = 2.
- Conventional liposarcoma = 2.
- Fibrosarcoma = 2.
- Myxofibrosarcoma =2.
A group of tumours is not graded:
- Alveolar soft part sarcoma.
- Clear cell sarcoma.
- Extraskeletal myxoid chondrosarcoma.
- 0-9 mitoses/10 HPF.
- 10-19 mitoses/10 HPF.
- >=20 mitoses/10 HPF.
- 1 HPF = 0.1734 mm^2.
- Most resident microscopes have a field of view = 0.2376 mm^2.
- Thus, ~7.3 HPFs on a resident microscope corresponds to 10 US-CAP HPFs.
- Most resident microscopes have a field of view = 0.2376 mm^2.
- None = score 0.
- <=50% of tumour = score 1.
- >50% of tumour = score 2.
System used by some at MSH
- Grade 1 = 1 point.
- Grade 2 = 2 points.
- Grade 3 = 3-4 points.
Points for each of the following:
- Mitotic activity >= 6 / 10 HPF @ 40X - definition suffers from HPFitis.
- Pleomorphism present.
- Cellularity (cells/matrix) > 50%.
- Necrosis >15% - microscopic (without targeting necrosis grossly) or grossly.
Lymph node metastases in sarcomas
- Lymph node (LN) spread is uncommon in sarcomas; lymph node metastases are seen in <3% of cases.
Sarcomas more likely to be found in the lymph nodes - mnemonic RACE For MS:
- Clear cell sarcoma.
- Epitheliod sarcoma.
- Malignant fibrous histiocytoma (pleomorphic undifferentiated sarcoma).
- Synovial cell sarcoma.
DDx by history/site
Young person - extremity sarcoma
- Usually non-specific.
- Most sarcomas have a pushing border.
- If there is an infiltrative border think: (1) fibromatosis, (2) carcinoma.
This category includes:
Smooth muscle tumours
IHC markers: desmin, SMA, H-caldemsin (most specific).
- Fasicular cellular spindle cell lesion with:
- Nuclear atypia.
- High mitotic rate.
Fibrohistiocytic refers (only) to the histomorphologic appearance and therefore may be written in quotation marks; these tumours are not derived from histiocytes (or tissue macrophages), as the name implies.
Pleomorphic undifferentiated sarcoma
- Abbreviated PUS.
- AKA Undifferentiated pleomorphic sarcoma, abbreviated UPS.
- Previously known as malignant fibrous histiocytoma, abbreviated MFH.
This is a very large and important group of soft tissue lesions. It is covered in a separate article.
The grouping includes:
- Inflammatory myofibroblastic tumour.
- Nodular fasciitis.
- Desmoid-type fibromatosis (Desmoid tumour).
- Proliferative fasciitis.
- Solitary fibrous tumour (Hemangiopericytoma).
- Desmoplastic fibroblastoma.
- Low-grade fibromyxoid sarcoma.
This grouping includes only two:
Vascular lesions are "too red"; they have too many RBCs.
Skeletal muscle tumours
- Abbreviated RMS.
Comes it two main flavours:
- Alveolar rhabdomyosarcoma.
- Embryonal rhabdomyosarcoma.
The histology may be that of a small round cell tumour.
Tumours of uncertain differentiation
Angiomatoid fibrous histiocytoma
- AKA deep aggressive angiomyxoma.
Extrarenal malignant rhabdoid tumour
- A small round blue cell tumour that may be seen in bone. It is discussed in the context of bone tumours.
- Sarcomas with an epithelioid morphology are covered in epithelioid sarcomas.
Alveolar soft part sarcoma
Desmoplastic small round cell tumour
Clear cell sarcoma
- Common alternate terms: extramedullary leukemia, myeloid sarcoma, chloroma.
- Other terms: myeloblastoma, chloromyeloma, chloromyelosarcoma, granulocytic leukosarcoma, or myelosarcoma.
- Spindle cell lesion.
- Small round cell tumours.
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