Angiomyolipoma / PEComa

Colon tumor
Mesenchymal tumors
Angiomyolipoma / PEComa

Author: Raul S. Gonzalez, M.D. (see Authors page)

Revised: 4 January 2017, last major update July 2016

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Angiomyolipoma [title] OR PEComa [title]

Table of Contents

Cite this page: Angiomyolipoma / PEComa. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/colontumoraml.html. Accessed July 14th, 2017.

Definition / general

Angiomyolipoma of colon: rare benign mesenchymal neoplasm, composed of vascular, adipocytic and smooth muscle elements, analogous to its more common counterpart in the kidney
PEComa: family of "perivascular epithelioid cell" neoplasms characterized by smooth muscle and melanocytic differentiation and positivity for HMB45; includes angiomyolipoma and PEComa-NOS

Essential features

Angiomyolipoma: bland triphasic mesenchymal neoplasm in the PEComa family; most reported colonic cases have been HMB45 negative (if stained), casting some doubt on the diagnosis
PEComa: epithelioid neoplasm with atypia and HMB45 positivity; "PEComa-NOS" may be the most appropriate diagnosis for these lesions

Terminology

PEComa-NOS cases have also been called "pleomorphic angiomyolipoma" (Int J Surg Pathol 2000;8:67)

Sites

Can arise anywhere in the gastrointestinal tract, though colon is most common

Clinical features

Patients typically middle aged, with a slight female predominance; they very rarely have tuberous sclerosis

Prognostic factors

Marked nuclear atypia, diffuse pleomorphism and high mitotic rate associated with risk of metastasis for PEComa (Am J Surg Pathol 2013;37:1769)

Case reports

54 year old man with large polypoid colon mass; bland and triphasic histologically and positive for HMB45 (Dis Colon Rectum 2003;46:547)
66 year old man with 5 cm pedunculated lesion; bland histologically, but negative for HMB45 (Clin Gastroenterol Hepatol 2005;3:A35)

Microscopic (histologic) description

Angiomyolipoma: bland mural tumor composed of smooth muscle, blood vessel and mature adipose elements
PEComa: mural tumor composed of large spindled or epithelioid cells with nuclear atypia and eosinophilic cytoplasm

Microscopic (histologic) images

Images hosted on other servers:

PEComa: spindled and epithelioid lesion with marked atypia

Positive stains

PEComa: SMA, desmin, HMB45, MelanA

Negative stains

Angiomyolipoma: HMB45 negative in nearly all reported examples (Am J Gastroenterol 1996;91:1852), unlike renal angiomyolipoma; this calls the diagnosis into doubt in such cases

Molecular / cytogenetics description

Tumors in the PEComa family are known to harbor TSC1, TSC2 and sometimes TFE3 mutations, though these have not specifically been demonstrated in the colon

Differential diagnosis

Alveolar soft part sarcoma: epithelioid, eosinophilic cells arranged in a nested / alveolar pattern; nuclei are bland and are positive for TFE3; all reported colonic cases appear to be metastases
Neuromuscular and vascular hamartoma: bland injury related proliferation of smooth muscle, vessels and nerves / ganglia; native fat may be present; more common in small intestine