Surgical Pathology Criteria

Proximal Type Epithelioid Sarcoma

Differential Diagnosis


Keratin positivity is typically seen in both
Squamous Carcinoma Proximal Type Epithelioid Sarcoma
CD34 negative CD34 50% positive
May have history of epithelial primary No primary epithelial lesion
Uncommon in young people Most patients under 40 years
May have in situ lesion or keratinization No in situ lesion or keratinization
CK5/6 commonly extensive CK5/6 rare, focal
CA125 negative in cutaneous SCC, frequently positive in SCC of other sites CA125 90%
CD34 reactivity is very rare in carcinoma of any type


Proximal Type Epithelioid Sarcoma Monophasic Synovial Sarcoma
Necrosis frequently extensive Necrosis usually focal
CD34 50% positive CD34 negative
No ropy collagen Ropy collagen frequent
Calcification infrequent Calcification frequent
No hemangiopericytomatous vessels Hemangiopericytomatous vessels frequent
No SYT-SSX gene fusion SYT-SST gene fusion present
Both may present as keratin positive spindle cell neoplasms


Epithelioid or rhabdoid cytoplasm may raise the following possibilities

Epithelioid Angiosarcoma Proximal Type Epithelioid Sarcoma
CD31 usually positive CD31 negative
May have adjacent atypical small channels No small atypical channels
  • CD34 and keratin may be positive in both.
  • Angiomatoid variant epithelioid sarcoma may be more difficult to distinguish as it may have large blood filled spaces.
  • Keratin positivity as well as cytoplasmic features may cause confusion between these two.

    Extrarenal Rhabdoid Tumor Proximal Type Epithelioid Sarcoma
    CD34 negative CD34 50% positive
    No intensely eosinophilic collagen Intensely eosinophilic collagen
    Median age 8-9 years Median age 35-40 years
    Wide range of sites Predilection for genitalia
    It is probable that malignant rhabdoid tumors do not occur in adults - most if not all are carcinoma, melanoma or proximal epithelioid sarcoma

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