Lung tumor
PEComa (clear cell tumor)

Topic Completed: 1 September 2016

Minor changes: 15 January 2020

Copyright: 2003-2020,, Inc.

PubMed Search: PEComa clear cell tumor lung

Roseann Wu, M.D., M.P.H.
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Cite this page: Wu R. PEComa (clear cell tumor). website. Accessed August 8th, 2020.
Definition / general
  • Benign/borderline peripheral lung neoplasm derived from perivascular epithelioid cells
  • Member of perivascular epithelioid cell tumor (PEComa) or "myomelanocytoma" family, which includes angiomyolipoma, lymphangioleiomyomatosis (LAM)
  • Grouped with LAM under PEComatous tumors in 2015 WHO Classification of Lung Tumors (J Thorac Oncol 2015;10:1243)
  • Sheets of large cells with clear to eosinophilic granular cytoplasm and PAS+ glycogen granules
Essential features
  • Extremely rare, benign pulmonary tumor derived from perivascular epithelioid cells (PEComa family of tumors)
  • Clear to eosinophilic, finely granular cytoplasm containing abundant PAS+ glycogen
  • Stains with melanocytic and smooth muscle markers by immunohistochemistry
  • First described as clear cell tumor of lung but also known as sugar tumor due to intracytoplasmic glycogen (Yale J Biol Med 1971;43:213)
  • Considered a benign PEComa in the lung, as opposed to malignant PEComa
ICD coding
  • D14.31 Benign neoplasm of right bronchus and lung
  • D14.32 Benign neoplasm of left bronchus and lung
  • D14.30 Benign neoplasm of unspecified bronchus and lung
  • Extremely rare, case reports and small case series
  • Generally older adults >40 years old, may occur in children
  • No clear gender predilection
  • Generally arises in peripheral lung, rarely in trachea or bronchi
  • May rarely arise in patients with tuberous sclerosis along with lymphangioleiomyomatosis (LAM) and micronodular pneumocyte hyperplasia (MMPH) (Am J Surg Pathol 1997;21:1242)
  • Mesenchymal perivascular epithelioid cells (PEComa family)
Clinical features
  • Generally asymptomatic or nonspecific pulmonary symptoms
  • Generally incidental finding on imaging
  • Requires tissue diagnosis with immunohistochemistry
Radiology description
Radiology images
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CT of clear cell tumor of lung

Prognosis and treatment
  • Rare case reports of malignant features and visceral metastasis
  • Aggressive features may include nuclear pleomorphism, >5 cm size, increased mitoses, necrosis (consider malignant PEComa)
Case reports
  • Simple surgical excision
Gross description
  • Small (<5 cm), sharply outlined, glistening, red-tan to brown mass, usually in peripheral lung
  • Uniform cut surface, though may have foci of necrosis
Gross images
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Well circumscribed tumors

4 cm, gray-white, circumscribed tumor
confined to the lower lobe under the pleura

Microscopic (histologic) description
  • Organoid (thick cords and rounded nests with sinusoid-type vascular network) or sheets of epithelioid cells
  • Clear to eosinophilic granular cytoplasm, well defined cell borders, numerous PAS+ glycogen granules
  • Small, uniform, rounded nuclei with small nucleoli, variably prominent sclerotic vasculature, may have extracellular amorphous eosinophilic material with variable calcification
  • Occasionally “spider cells” with nuclear condensation of eosinophilic cytoplasm with extensions to the cell membrane
  • May show entrapped small airways, necrosis, sparse lymphocytes
  • No fat, no / rare mitoses
  • Rarely malignant features (J Clin Oncol 2010;28:e626, Histopathology 2011;58:498)
Microscopic (histologic) images
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(A) Core needle biopsy shows neoplastic cells in nested and insular pattern surrounding numerous thinned wall sinusoid-like vessels
(B) intranuclear cytoplasmic invaginations
(C) HMB45+ staining

Tumor with malignant histiology

Various images

Cytology description
  • Small and large cohesive clusters of bland epithelioid to spindle cells with oval or elongated nuclei, indistinct nucleoli, finely vacuolated cytoplasm, delicate transgressing vessels, background naked nuclei, rare intranuclear pseudoinclusion (Diagn Cytopathol 2008;36:89)
Cytology images
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Benign sclerosing perivascular epithelioid cell tumor (PEComa)

(A) Large, irregular, cohesive clusters of columnar and spindle-shaped cells in background of single naked nuclei (Pap)
(B) several large clusters with open cribriform-like spaces (Pap)
(C) spindle-shaped and polygonal cells with round to oval nuclei and vacuolated ill-defined cytoplasm (Pap)
(D) cell block shows neoplastic cells arranged in a nested and insular pattern surrounding sinusoid-like vessels; inset shows sinusoid-like vessel amidst tumor

Negative stains
Electron microscopy description
Molecular / cytogenetics description
  • TSC2 loss of heterozygosity when arises in patient with tuberous sclerosis
Differential diagnosis
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