Soft tissue

General

WHO classification


Editorial Board Member: Nasir Ud Din, M.B.B.S.
Borislav A. Alexiev, M.D.

Minor changes: 3 January 2022

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PubMed Search: Soft tissue WHO classification[TI]

Borislav A. Alexiev, M.D.
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Cite this page: Alexiev BA. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuewhoclassification.html. Accessed January 21st, 2022.
Definition / general
  • WHO classification of soft tissue tumors serves as a guide to clarify diagnoses among a multidisciplinary team composed of pathologists, radiologists and clinicians (Adv Anat Pathol 2021;28:44)
Major updates
  • Adipocytic tumors
    • 2 new entities are considered in the new classification: atypical spindle cell / pleomorphic lipomatous tumor and myxoid pleomorphic liposarcoma
    • Benign
    • Malignant
    • Extrarenal angiomyolipoma was deleted in this category and reclassified in the category of tumors of uncertain differentiation and is now referred to as angiomyolipoma (Adv Anat Pathol 2021;28:44)
    • Extra-adrenal myelolipoma was removed in this edition
  • Fibroblastic and myofibroblastic tumors
  • So called fibrohistiocytic tumors
    • Most relevant entity that has disappeared since 2013 is represented by the family of so called malignant fibrous histiocytoma (MFH) (Pathologica 2021;113:70)
      • Undifferentiated pleomorphic sarcoma currently represents the correct designation for the storiform and pleomorphic variant of MFH
      • Giant cell MFH is currently replaced by 3 distinct tumor types: giant cell tumor of soft tissues, extraskeletal osteosarcoma and giant cell rich osteosarcoma (Pathologica 2021;113:70)
      • Myxoid MFH is currently recognized as a purely fibroblastic tumor, identified with the original name myxofibrosarcoma (Pathologica 2021;113:70)
      • Inflammatory MFH overlaps entirely with the inflammatory variant of dedifferentiated liposarcomas (Pathologica 2021;113:70)
      • Angiomatoid MFH (an indolent lesion most often harboring a EWSR1-CREB1 fusion gene and more rarely a EWSR1-ATF1 or FUS-ATF1 fusion gene) is currently listed within the group of soft tissue lesion of unknown differentiation (Pathologica 2021;113:70, Clin Cancer Res 2007;13:7322)
  • Vascular tumors
  • Smooth muscle tumors
    • 2 new entities are considered in the new classification: EBV associated smooth muscle tumors and inflammatory leiomyosarcoma (Pathologica 2021;113:70)
    • Intermediate
    • Malignant
  • Peripheral nerve sheath tumors
    • Single major change introduced by the 2020 WHO classification is the recognition that so called melanotic schwannoma actually represents a clinically aggressive neoplasm (no longer belonging to the intermediate category) and is consequently relabeled as malignant melanotic nerve sheath tumor (Pathologica 2021;113:70)
    • Malignant
  • Tumors of uncertain differentiation
    • NTRK rearranged spindle cell neoplasms (excluding infantile fibrosarcoma that represent a distinct clinicopathologic entity defined molecularly by the presence of NTRK3-ETV6 fusion gene) represent an emerging group of molecularly defined rare soft tissue tumors (Pathologica 2021;113:70)
    • Prognosis of NTRK rearranged adult tumors appear to be related to histological grade
    • NTRK rearranged spindle cell neoplasm
  • Undifferentiated small round cell sarcoma of bone and soft tissue
WHO (2020)











    Undifferentiated small round cell sarcoma of bone and soft tissue ICD-O
  • Ewing sarcoma9364/3
  • Round cell sarcoma with EWSR1 non-ETS fusions9366/3
  • CIC rearranged sarcoma9367/3
  • Sarcoma with BCOR genetic alterations9368/3
Diagrams / tables
None
Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D.
Myxoid liposarcoma

Myxoid liposarcoma

Pleomorphic liposarcoma

Pleomorphic liposarcoma

Inflammatory leiomyosarcoma

Inflammatory leiomyosarcoma

Sclerosing epithelioid fibrosarcoma

Sclerosing epithelioid fibrosarcoma

Biphasic synovial sarcoma

Biphasic synovial sarcoma

Proximal type epithelioid sarcoma

Proximal type epithelioid sarcoma


Extraskeletal myxoid chondrosarcoma

Extraskeletal myxoid chondrosarcoma

Alveolar soft part sarcoma

Alveolar soft part sarcoma

Clear cell sarcoma

Clear cell sarcoma

Desmoplastic small round cell tumor

Desmoplastic small round cell tumor

CIC rearranged sarcoma

CIC rearranged sarcoma

Sarcoma with BCOR genetic alterations

Sarcoma with BCOR genetic alterations

Board review style question #1
The single new entity appearing among vascular lesions in the WHO 2020 classification is named anastomosing hemangioma. What is the most common site of anastomosing hemangioma?

  1. Head and neck
  2. Intestinal tract
  3. Kidney and retroperitoneal adipose tissue
  4. Limbs
  5. Lungs and uterus
Board review style answer #1
C. Kidney and retroperitoneal adipose tissue

Comment Here

Reference: WHO classification of soft tissue tumors
Board review style question #2

The histologic pattern shown above would be most commonly expected in which of the following soft tissue tumors listed in WHO 2020?

  1. Cellular angiofibroma
  2. Low grade fibromyxoid sarcoma
  3. Myofibroblastoma
  4. Perineurioma
  5. Solitary fibrous tumor
Board review style answer #2
E. Solitary fibrous tumor. Solitary fibrous tumor is characterized by haphazardly arranged spindled to ovoid cells with indistinct, pale eosinophilic cytoplasm within a variably collagenous stroma and branching staghorn vascular pattern (hemangiopericytomatous vessels).

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Reference: WHO classification of soft tissue tumors
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