Home » What is SARCOMA? » Soft Tissue Sarcoma Reference Guide » Aggressive Soft Tissue Sarcoma of Uncertain Differentiation
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Alternative diagnostic termsIncludes Classic/Distal and Proximal variants
Common anatomical locationsClassic/Distal type occurs in the peripheral upper extremity, predominantly arising in the fingers and hand while the Proximal large cell type occurs in the proximal (upper) extremities, pelvis, or shoulder.
Pathology commentTwo clinicopathological subtypes are recognized: the classic (or distal) form, characterized by its proclivity for acral (peripheral) sites and pseudogranulomatous growth pattern, and the proximal-type (large cell) subtype, which arises mainly in proximal/truncal regions and consists of nests and sheets of large epithelioid cells.
SourceFletcher CDM, Oda Y, Nielsen TO, Dal Cin P, François LL. Epithelioid Sarcoma. In: WHO Classification of Tumors Editorial Board. Soft tissue and bone tumors [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [2024 Dec 29]. (WHO Classification of Tumors Series, 5th ed.; vol. 3). Available from: https://tumorclassification.iarc.who.int/chapters/33
For diagnosis or treatmentAny center listed in the Sarcoma Center Directory »
Patient advocacyAny organization with an established program for patient triage, support, and education. See Patient Support Organizations »
Clinical trialsSARC Clinical Trials – NoneFind other clinical studies registered on ClinicalTrials.gov
Alternative diagnostic termsNone
Common anatomical locationsNone
Pathology commentUSTS shows no identifiable line of differentiation when analyzed by presently available technology. Spindle, pleomorphic, epithelioid, and round cell (most often high-grade) morphology; demonstrated absence of distinctive molecular aberration.
SourceFletcher CDM, Paolo Dei Tos A, Mertens F, Pillay N. Undifferentiated Sarcoma. In: WHO Classification of Tumors Editorial Board. Soft tissue and bone tumors [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [2024 Dec 29]. (WHO Classification of Tumors Series, 5th ed.; vol. 3). Available from: https://tumorclassification.iarc.who.int/chapters/33
For diagnosis or treatmentAny center listed as a SARC Honor Roll member in the Sarcoma Centers Directory »
Clinical trialsSARC Clinical Trials – None Find other clinical studies registered on ClinicalTrials.gov
Pending: Current SARC Pathology project recreating a UPS diagnostic map.
Common anatomical locationsDeep-seated sites in the extremity, with 50% of cases arising in the distal lower extremity, ankle, or foot.
Pathology commentMost often characterized by EWSR1-ATF1 fusion, harboring a distinctive nested growth pattern and melanocytic differentiation.
SourceFletcher CDM, Fritchie KJ, van de Rijn M. Clear Cell Sarcoma. In: WHO Classification of Tumors Editorial Board. Soft tissue and bone tumors [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [2024 Dec 29]. (WHO Classification of Tumors Series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/login?redirecturl=%2Fchapters%2F33
For diagnosis or treatmentAny center listed in the Sarcoma Centers Directory »
Common anatomical locationsDeep soft tissues of the extremities 61% in the lower extremities, 51% in the trunk, 20% in internal organs (8%), and 9% in the head and neck. Typical tumor for adolescents & young adults.
Pathology commentCharacterized by the defining genetic feature for ASPS, a der(17)t(X;17)(p11.2;q25) translocation which results in a fusion between ASPSCR1-TFE3 gene fusion (chromosome 17) and the TFE3 gene on the X chromosome creating the ASPSCR1-TFE3 fusion protein.
SourceFletcher CDM, Jambhekar N, Ladanyi M. Alveolar soft part Sarcoma. In: WHO Classification of Tumors Editorial Board. Soft tissue and bone tumors [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [2024 Dec 29]. (WHO Classification of Tumors Series, 5th ed.; vol. 3). Available from: https://tumorclassification.iarc.who.int/chapters/33.G