WHO classification of tumors of soft tissue

The World Health Organization (WHO) classification of soft tissue tumors is the most widely used pathology-based classification system for such disorders. The current revision, part of the 5th edition of the WHO classification of soft tissue and bone tumors (volume 3), was published in 2020 and is reflected in the article below ¹.

Classification

Adipocytic tumors

• lipoma

• lipomatosis

• lipomatosis of nerve

• lipoblastoma and lipoblastomatosis

• angiolipoma

• myolipoma of soft tissue

• chondroid lipoma

• spindle cell/pleomorphic lipoma

• hibernoma

• atypical spindle cell/pleomorphic lipomatous tumor

• atypical lipomatous tumor/well-differentiated liposarcoma

• dedifferentiated liposarcoma

• myxoid liposarcoma

• pleomorphic liposarcoma

• myxoid pleomorphic liposarcoma

Fibroblastic/myofibroblastic tumors

• nodular fasciitis

• proliferative fasciitis and proliferative myositis

• myositis ossificans and fibro-osseous pseudotumor of digits

• ischemic fasciitis

• elastofibroma

• fibrous hamartoma of infancy

• fibromatosis colli

• juvenile hyaline fibromatosis

• inclusion body fibromatosis

• fibroma of tendon sheath

• desmoplastic fibroblastoma

• myofibroblastoma

• calcifying aponeurotic fibroma

• EWSR1-SMAD3-positive fibroblastic tumor (emerging)

• angiomyofibroblastoma

• cellular angiofibroma

• angiofibroma of soft tissue

• acral fibromyxoma

• nuchal-type fibroma

• Gardner fibroma

• calcifying fibrous tumor

• palmar/plantar fibromatosis

• desmoid-type fibromatosis

• lipofibromatosis

• giant cell fibroblastoma

• dermatofibrosarcoma protuberans

• solitary fibrous tumor

• inflammatory myofibroblastic tumor

• low-grade myofibroblastic sarcoma

• superficial CD34-positive fibroblastic tumor

• myxoinflammatory fibroblastic sarcoma

• infantile fibrosarcoma

• adult fibrosarcoma

• myxofibrosarcoma

• low-grade fibromyxoid sarcoma

• sclerosing epithelioid fibrosarcoma

So-called fibrohistiocytic tumors

• tenosynovial giant cell tumor

• deep benign fibrous histiocytoma

• plexiform fibrohistiocytic tumor

• giant cell tumor of soft tissue

Vascular tumors

• hemangiomas

  • synovial hemangioma

  • intramuscular hemangioma

  • arteriovenous malformation/hemangioma

  • venous hemangioma

• anastomosing hemangioma

• epithelioid hemangioma

• lymphangioma and lymphangiomatosis

• tufted angioma and Kaposiform hemangioendothelioma

• retiform hemangioendothelioma

• papillary intralymphatic angioendothelioma

• composite hemangioendothelioma

• Kaposi sarcoma

• pseudomyogenic hemangioendothelioma

• epithelioid hemangioendothelioma

• angiosarcoma

Pericytic (perivascular) tumors

• glomangioma

• myopericytoma, including myofibroma

• angioleiomyoma

Smooth muscle tumors

• leiomyoma of deep soft tissue

• EBV-associated smooth muscle tumor

• inflammatory leiomyosarcoma

• leiomyosarcoma

Skeletal-muscle tumors

• rhabdomyoma

• embryonal rhabdomyosarcoma

• alveolar rhabdomyosarcoma

• pleomorphic rhabdomyosarcoma

• spindle cell/sclerosing rhabdomyosarcoma

• ectomesenchymoma

Gastrointestinal stromal tumors

• gastrointestinal stromal tumors

Chondro-osseous tumors

• soft-tissue chondroma

• extraskeletal osteosarcoma

Peripheral nerve sheath tumors

• schwannoma (including variants)

• neurofibroma (including variants)

• perineurioma

• granular cell tumor

• dermal nerve sheath myxoma

• solitary circumscribed neuroma

• ectopic meningioma and meningothelial hamartoma

• benign triton tumor/neuromuscular choristoma

• hybrid nerve sheath tumors

• malignant peripheral nerve sheath tumor

• malignant melanotic nerve sheath tumor

Tumors of uncertain differentiation

• intramuscular myxoma

• juxta-articular myxoma

• deep ("aggressive") angiomyxoma

• atypical fibroxanthoma

• angiomatoid fibrous histiocytoma

• ossifying fibromyxoid tumor

• myoepithelioma/myoepithelial carcinoma/mixed tumor

• pleomorphic hyalinizing angiectatic tumor of soft parts

• haemosiderotic fibrolipomatous tumor

• phosphaturic mesenchymal tumor

• NTRK-rearranged soft tissue neoplasms

• synovial sarcoma

• epithelioid sarcoma

• alveolar soft part sarcoma

• clear cell sarcoma of soft tissue

• extraskeletal myxoid chondrosarcoma

• desmoplastic small round cell tumor

• extrarenal rhabdoid tumor

• PEComa

• intimal sarcoma

• undifferentiated sarcoma

Changes from the prior version

New entities and variants

Newly introduced entities include the following ^1-5:

• adipocytic tumors

  • atypical spindle cell/pleomorphic lipomatous tumor

  • myxoid pleomorphic liposarcoma

• fibroblastic and myofibroblastic tumors

  • angiofibroma of soft tissue

  • superficial CD34-positive fibroblastic tumor

  • EWSR-SMAD3-positive fibroblastic tumor

• vascular tumors

  • epithelioid hemangioendothelioma features two newly recognized subtypes

  • anastomosing hemangioma

  • tufted angioma and Kaposiform hemangioendothelioma are classified together

• pericytic (perivascular) tumors

  • myopericytoma, including myofibroma - new subtype: cellular myofibroma/myopericytoma

• smooth muscle tumors

  • EBV-associated smooth muscle tumor

  • inflammatory leiomyosarcoma

• skeletal muscle tumors

  • spindle cell/sclerosing rhabdomyosarcoma - three subtypes

• tumors of uncertain differentiation

  • NTRK-rearranged soft tissue neoplasms

Other changes

• melanotic schwannoma: now renamed to malignant melanotic nerve sheath tumor

• dedifferentiated liposarcoma: adverse prognostic impact of myogenic and rhabdomyoblastic differentiation as well of a high grade on the FNCLCC (French Federation of Cancer Centers Sarcoma Group) grading system

• solitary fibrous tumor: 'extrapleural' has been removed