Soft tissue
Uncertain differentiation

Topic Completed: 1 November 2012

Minor changes: 15 July 2020

Copyright: 2002-2019,, Inc.

PubMed Search: PEComa [title] soft tissue

Vijay Shankar, M.D.
Page views in 2019: 16,987
Page views in 2020 to date: 10,131
Cite this page: Shankar V. PEComa-general. website. Accessed August 14th, 2020.
Definition / general
  • Mesenchymal tumor with perivascular clear cell and epithelioid features that coexpresses melanocytic and muscle markers
  • Concept first proposed by Bonetti (Am J Surg Pathol 1992;16:307)
  • Tumor family includes angiomyolipoma (renal and extrarenal), clear cell "sugar" tumor (lung and extrapulmonary) and lymphangioleiomyomatosis; these tumors are relatively common and are associated with tuberous sclerosis
  • Family also includes tumors of falciform ligament / ligamentum teres, skin (Histopathology 2005;46:498), uterus (Mod Pathol 2005;18:1336) and other viscera and soft tissue; these tumors are rare, and are not associated with tuberous sclerosis
  • No known normal counterpart to the perivascular epithelioid cell
Prognostic factors
  • Usually benign, but some cases have malignant behavior and simulate high grade sarcoma (Pathology 2006;38:415)
  • Poor prognostic factors: tumor size > 5 - 8 cm, infiltrative growth pattern, high nuclear grade, > 1 mitotic figure / 50 HPF or atypical mitotic figures, coagulative cell necrosis (Am J Surg Pathol 2005;29:1558)
Case reports
  • Excision is usually curative if tumors are benign
Clinical images

Images hosted on PathOut servers:

Cutaneous, courtesy of Mark R. Wick, M.D.

Gross images

Images hosted on PathOut servers:

Buttocks, courtesy of Mark R. Wick, M.D.

Images hosted on other servers:

Uterus: polypoid mass

Microscopic (histologic) description
  • Perivascular tumor cells may have radial arrangement around lumen; epithelioid cells (closest to vessel) and spindle cells (remote from vessel) with clear to granular eosinophilic cytoplasm; small, central, round / oval nuclei with small nucleoli; often multinucleated giant cells; may have malignant features with marked atypia, mitotic activity and necrosis
  • Pecosis: continuous layer of perivascular clear cells remote from tumor, transitioning to invasive nests and PEComa; cells are in apposition to and in direct contact with abluminal surface of capillary basal lamina (Virchows Arch 2007;450:463)
  • Pecomatosis: nests of perivascular clear to eosinophilic cells (World J Surg Oncol 2004;2:35); may simulate mesothelioma (Ann Diagn Pathol 2006;10:352)
Microscopic (histologic) images

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Images hosted on PathOut servers:
Soft tissue (Case of the Week #283):

Alpha smooth muscle actin

HMB45 - low power

HMB45 - high power

Courtesy of Mark R. Wick, M.D.:

Soft tissue angiomyolipoma


Images hosted on other servers:

Epithelioid cells


Smooth muscle actin+


Mass with central circular core

Infiltrative border

Spindled to epithelioid areas

Degenerative atypia


Ovarian hila


Head and neck:

Nasal PEComa



Malignant epithelioid cells

Positive stains
Negative stains
Electron microscopy description
  • Abundant cytoplasmic glycogen, premelanosomes, thin filaments with occasional dense bodies, hemidesmosomes, poorly formed cellular junctions
Molecular / cytogenetics description
  • Gross chromosomal aberrances in most / all cases; most frequent imbalances are 19-, 16p-, 17p-, 1p-, 18p-, X+, 12q+, 3q+, 5+, 2q+; 16p- indicates loss of TSC2 gene (Hum Pathol 2006;37:606)
Differential diagnosis
  • Clear cell / oxyphilic carcinoma: cytokeratin+
  • Epithelioid / clear cell smooth muscle tumors: HMB45-
  • Melanoma: strong S100+
  • Undifferentiated / high grade sarcoma
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