Soft tissue
General
WHO classification
Author: Borislav A. Alexiev, M.D.
Editorial Board Member: Nasir Ud Din, M.B.B.S.
Last author update: 6 June 2022
Last staff update: 30 December 2024
Copyright: 2022-2025, PathologyOutlines.com, Inc.
PubMed Search: Soft tissue WHO classification[TI]
Table of Contents
Definition / general | Major updates | WHO (2020) | Microscopic (histologic) images | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Alexiev BA. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuewhoclassification.html. Accessed April 1st, 2025.
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
- Atypical spindle cell / pleomorphic lipomatous tumor (ASPLT) (Adv Anat Pathol 2021;28:44, Pathologica 2021;113:70)
- Malignant
- Myxoid pleomorphic liposarcoma (Adv Anat Pathol 2021;28:44, Am J Surg Pathol 2009;33:645)
- 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
- 3 new benign entities are considered in the new classification
- Benign
- Angiofibroma of soft tissue (Am J Surg Pathol 2012;36:500)
- EWSR1-SMAD3 fibroblastic tumor (Am J Surg Pathol 2018;42:522)
- Superficial CD34 positive fibroblastic tumor (Mod Pathol 2014;27:294)
- 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)
- Most relevant entity that has disappeared since 2013 is represented by the family of so called malignant fibrous histiocytoma (MFH) (Pathologica 2021;113:70)
- Vascular tumors
- Benign
- Single new entity appearing among vascular lesions is named anastomosing hemangioma (Pathologica 2021;113:70, Am J Surg Pathol 2009;33:1364)
- Benign
- 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
- EBV associated smooth muscle tumor / smooth muscle tumor of uncertain malignant potential (Front Immunol 2018;9:368)
- Malignant
- Inflammatory leiomyosarcoma (Mod Pathol 2018;31:93)
- 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
- Malignant melanotic nerve sheath tumor (Am J Surg Pathol 2014;38:94)
- 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
- This provisional category includes the recently described lipofibromatosis-like neural tumor and NTRK rearranged neoplasm resembling peripheral nerve sheath tumors (Am J Surg Pathol 2016;40:1407, Genes Chromosomes Cancer 2018;57:611, Am J Surg Pathol 2019;43:435, J Pathol 2016;238:700)
- Undifferentiated small round cell sarcoma of bone and soft tissue
- This new section contains not only the prototypical round cell sarcoma named Ewing sarcoma but also 3 distinct subsets that differs from Ewing sarcoma clinically, pathologically and molecularly (Pathologica 2021;113:70):
- Round cell sarcomas with EWSR1 gene fusion with non-ETS family members (Virchows Arch 2020;476:109, Am J Surg Pathol 2019;43:1112, Am J Surg Pathol 2019;43:220, Mod Pathol 2019;32:1593)
- CIC rearranged sarcomas (Genes Chromosomes Cancer 2012;51:207, Am J Surg Pathol 2017;41:941)
- BCOR rearranged sarcomas (Am J Surg Pathol 2018;42:604)
- This new section contains not only the prototypical round cell sarcoma named Ewing sarcoma but also 3 distinct subsets that differs from Ewing sarcoma clinically, pathologically and molecularly (Pathologica 2021;113:70):
WHO (2020)
-
Adipocytic tumors ICD-O
- Benign
- Lipoma, NOS8850/0
- Intramuscular lipoma8856/0
- Chondrolipoma
- Lipomatosis
- Diffuse lipomatosis
- Multiple symmetrical lipomatosis
- Pelvic lipomatosis
- Steroid lipomatosis
- HIV lipodystrophy
- Lipomatosis of nerve
- Lipoblastomatosis8881/0
- Angiolipoma, NOS8861/0
- Cellular angiolipoma
- Myolipoma8890/0
- Chondroid lipoma8862/0
- Spindle cell lipoma8857/0
- Atypical spindle cell / pleomorphic lipomatous tumor 8857/0
- Hibernoma8880/0
- Lipoma, NOS8850/0
- Intermediate (locally aggressive)
- Malignant
- Liposarcoma, well differentiated, NOS8851/3
- Lipoma-like liposarcoma8851/3
- Inflammatory liposarcoma8851/3
- Sclerosing liposarcoma8851/3
- Dedifferentiated liposarcoma8858/3
- Myxoid liposarcoma8852/3
- Pleomorphic liposarcoma8854/3
- Myxoid pleomorphic liposarcoma8859/3
- Liposarcoma, well differentiated, NOS8851/3
-
Fibroblastic and myofibroblastic tumors ICD-O
- Benign
- Nodular fasciitis8828/0
- Intravascular fasciitis
- Cranial fasciitis
- Proliferative fasciitis8828/0
- Proliferative myositis8828/0
- Elastofibroma8820/0
- Fibrous hamartoma of infancy8992/0
- Fibromatosis colli
- Juvenile hyaline fibromatosis
- Inclusion body fibromatosis
- Fibroma of tendon sheath8813/0
- Demoplastic fibroblastoma8810/0
- Myofibroblastoma8825/0
- Calcifying aponeurotic fibroma8816/0
- EWSR1-SMAD3 positive fibroblastic tumor (emerging)
- Angiomyofibroblastoma8826/0
- Cellular angiofibroma9160/0
- Angiofibroma, NOS9160/0
- Nuchal fibroma8810/0
- Acral fibromyxoma8811/0
- Gardner fibroma8810/0
- Nodular fasciitis8828/0
- Intermediate (locally aggressive)
- Solitary fibrous tumor, benign8815/0
- Palmar / plantar type fibromatosis8813/1
- Desmoid type fibromatosis8821/1
- Extra-abdominal desmoid8821/1
- Abdominal fibromatosis8822/1
- Lipofibromatosis8851/1
- Giant cell fibroblastoma8834/1
- Intermediate (rarely metastasizing)
- Dermatofibrosarcoma protuberans, NOS8832/1
- Pigmented dermatofibrosarcoma protuberans8833/1
- Dermatofibrosarcoma protuberans, fibrosarcomatous8832/3
- Myxoid dermatofibrosarcoma protuberans
- Dermatofibrosarcoma protuberans with myoid differentiation
- Plaque-like dermatofibrosarcoma protuberans
- Solitary fibrous tumor, NOS8815/1
- Inflammatory myofibroblastic tumor8825/1
- Myofibroblastic sarcoma8825/3
- Superficial CD34 positive fibroblastic tumor8810/1
- Myxoinflammatory fibroblastic sarcoma8811/1
- Infantile fibrosarcoma8814/3
- Dermatofibrosarcoma protuberans, NOS8832/1
- Malignant
- Solitary fibrous tumor, malignant8815/3
- Fibrosarcoma, NOS8810/3
- Myxofibrosarcoma8811/3
- Low grade fibromyxoid sarcoma8840/3
- Sclerosing epithelioid fibrosarcoma8840/3
-
So called fibrohistiocytic tumors ICD-O
- Benign
- Intermediate (rarely metastasizing)
- Malignant
-
Vascular tumors ICD-O
- Benign
- Hemangioma, NOS9120/0
- Intramuscular hemangioma9132/0
- Arteriovenous hemangioma9123/0
- Venous hemangioma9122/0
- Anastomosing hemangioma9120/0
- Epithelioid hemangioma9125/0
- Cellular epithelioid hemangioma
- Atypical epithelioid hemangioma
- Lymphangioma, NOS9170/0
- Cystic lymphangioma9173/0
- Acquired tufted hemangioma9161/0
- Intermediate (locally aggressive)
- Intermediate (rarely metastasizing)
- Retiform hemangioendothelioma9136/1
- Papillary intralymphatic angioendothelioma9135/1
- Composite hemangioendothelioma9136/1
- Neuroendocrine composite hemangioendothelioma
- Kaposi sarcoma9140/3
- Pseudomyogenic (epithelioid sarcoma-like) hemangioendothelioma9138/1
- Malignant
-
Pericytic (perivascular) tumors ICD-O
- Benign and intermediate
- Glomus tumor, NOS8711/0
- Glomangioma8712/0
- Glomangiomyoma8713/0
- Glomangiomatosis8711/1
- Glomus tumor of uncertain malignant potential8711/1
- Myopericytoma8824/0
- Myofibromatosis8824/1
- Myofibroma8824/0
- Infantile myofibromatosis8824/1
- Angioleiomyoma8894/0
- Glomus tumor, NOS8711/0
- Malignant
- Glomus tumor, malignant8711/3
-
Smooth muscle tumors ICD-O
- Benign and intermediate
- Malignant
- Leiomyosarcoma, NOS8890/3
- Inflammatory leiomyosarcoma8890/3
-
Skeletal muscle tumors ICD-O
- Benign
- Rhabdomyoma, NOS 8900/0
- Fetal rhabdomyoma8903/0
- Adult rhabdomyoma8904/0
- Genital rhabdomyoma8905/0
- Rhabdomyoma, NOS 8900/0
- Malignant
- Embryonal rhabdomyosarcoma, NOS8910/3
- Embryonal rhabdomyosarcoma, pleomorphic8920/3
- Alveolar rhabdomyosarcoma8910/3
- Pleomorphic rhabdomyosarcoma, NOS8901/3
- Spindle cell rhabdomyosarcoma, NOS8912/3
- Ectomesenchymoma8921/3
- Embryonal rhabdomyosarcoma, NOS8910/3
-
Gastrointestinal stromal tumors ICD-O
-
Chondro-osseous tumors ICD-O
- Benign
- Chondroma, NOS8922/0
- Chondroblastoma-like soft tissue chondroma
- Chondroma, NOS8922/0
- Malignant
-
Peripheral nerve sheath tumors ICD-O
- Benign
- Schwannoma, NOS9560/0
- Ancient schwannoma9560/0
- Cellular schwannoma9560/0
- Plexiform schwannoma9560/0
- Epithelioid schwannoma
- Microcystic / reticular schwannoma
- Neurofibroma, NOS9540/0
- Ancient neurofibroma
- Cellular neurofibroma
- Atypical neurofibroma
- Plexiform neurofibroma9550/0
- Perineurioma, NOS9571/0
- Reticular perineurioma
- Sclerosing perineurioma
- Granular cell tumor, NOS9580/0
- Nerve sheath myxoma9562/0
- Solitary circumscribed neuroma9570/0
- Plexiform solitary circumscribed neuroma
- Meningioma, NOS9530/0
- Benign triton tumor / neuromuscular choristoma
- Hybrid nerve sheath tumor9563/0
- Perineurioma / schwannoma
- Schwannoma / neurofibroma
- Perineurioma / neurofibroma
- Schwannoma, NOS9560/0
- Malignant
- Malignant peripheral nerve sheath tumor, NOS9540/3
- Malignant peripheral nerve sheath tumor, epithelioid9542/3
- Melanotic malignant peripheral nerve sheath tumor9540/3
- Granular cell tumor, malignant9580/3
- Perineurioma, malignant9571/3
- Malignant peripheral nerve sheath tumor, NOS9540/3
-
Tumors of uncertain differentiation ICD-O
- Benign
- Myxoma, NOS8840/0
- Cellular myxoma
- Aggressive angiomyxoma8841/0
- Pleomorphic hyalinizing angiectatic tumor8802/1
- Phosphaturic mesenchymal tumor, NOS8990/0
- Perivascular epithelioid tumor, benign8714/0
- Angiomyolipoma8860/0
- Myxoma, NOS8840/0
- Intermediate (locally aggressive)
- Hemosiderotic fibrolipomatous tumor8811/1
- Angiomyolipoma, epithelioid8860/1
- Intermediate (rarely metastasizing)
- Atypical fibroxanthoma8830/1
- Angiomatoid fibrous histiocytoma8836/1
- Ossifying fibromyxoid tumor, NOS8842/0
- Mixed tumor, NOS8940/0
- Mixed tumor, malignant, NOS8940/3
- Myoepithelioma, NOS8982/0
- Malignant
- Phosphaturic mesenchymal tumor, malignant8990/3
- NTRK rearranged spindle cell neoplasm (emerging)
- Synovial sarcoma, NOS9040/3
- Epithelioid sarcoma8804/3
- Alveolar soft part sarcoma9581/3
- Clear cell sarcoma, NOS9044/3
- Extraskeletal myxoid chondrosarcoma9231/3
- Desmoplastic small round cell tumor8806/3
- Rhabdoid tumor, NOS8963/3
- Perivascular epithelioid tumor, malignant8714/3
- Intimal sarcoma9137/3
- Ossifying fibromyxoid tumor, malignant8842/3
- Myoepithelial carcinoma8982/3
- Undifferentiated sarcoma8805/3
- Spindle cell sarcoma, undifferentiated8801/3
- Pleomorphic sarcoma, undifferentiated8802/3
- Round cell sarcoma, undifferentiated8803/3
- Phosphaturic mesenchymal tumor, malignant8990/3
-
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
Microscopic (histologic) images
Contributed by Borislav A. Alexiev, M.D.
Myxoid liposarcoma
Pleomorphic liposarcoma
Inflammatory leiomyosarcoma
Sclerosing epithelioid fibrosarcoma
Biphasic synovial sarcoma
Proximal type epithelioid sarcoma
Extraskeletal myxoid chondrosarcoma
Alveolar soft part sarcoma
Clear cell sarcoma
Desmoplastic small round cell tumor
CIC rearranged sarcoma
Sarcoma with BCOR genetic alterations
Additional references
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?
- Head and neck
- Intestinal tract
- Kidney and retroperitoneal adipose tissue
- Limbs
- Lungs and uterus
Board review style answer #1
C. Kidney and retroperitoneal adipose tissue
Comment Here
Reference: WHO classification of soft tissue tumors
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?
- Cellular angiofibroma
- Low grade fibromyxoid sarcoma
- Myofibroblastoma
- Perineurioma
- 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).
Comment Here
Reference: WHO classification of soft tissue tumors
Comment Here
Reference: WHO classification of soft tissue tumors
