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Uterus (excludes Cervix)

Epithelial tumors

Perivascular epithelioid cell tumor (PEComa)

Reviewer: Mohamed Mokhtar Desouki, MD, PhD (see Reviewers page)
Revised: 22 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Poorly defined, rare tumors characterized by varying amounts of epithelioid and spindle cells with clear to eosinophilic, granular cytoplasm that is HMB45+ in a diffuse or focal pattern
● Tumors are morphologically and immunophenotypically similar to the perivascular epithelioid cells of epithelioid angiomyolipoma, clear cell (“sugar”) tumor, clear cell myomelanocytic tumor of ligamentum teres/falciform ligament and abdominopelvic sarcoma of perivascular epithelioid cells, and a subset of the cells in some examples of lymphangioleiomyomatosis (click here for soft tissue tumor chapter)
● Only PEComas of the uterine corpus were recognized in the 2003 WHO classication of gynecologic neoplasms

Epidemiology
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● Mean age of 45 years (range, 9-79 years)
● ~50 cases reported in English-language literature

Sites
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● Uterus and retroperitoneum

Etiology
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● Etiology unknown; tumors may be associated with tuberous sclerosis complex (~9% of cases reported)

Clinical features
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● Abnormal uterine bleeding, uterine mass, abdominal pain, hemoperitoneum or hydrosalpinx
● Considered a tumor of uncertain malignant potential (Am J Surg Pathol 2002;26:1)
● May exhibit aggressive behavior and recur after hysterectomy

Treatment
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● Hysterectomy, with or without adjuvant chemotherapy and radiotherapy

Gross description
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● Solitary or rarely multifocal mass in uterine corpus from 0.6 to 12.0 cm (mean of 4.7 cm)
● Cut sections may be gray–white, tan or yellow with whorled or soft, fleshy, ill-defined, or rarely circumscribed margins

Gross images
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Polypoid mass

Micro description
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● Tumors divided into two groups (A and B), each of which is either benign or malignant
● Group A demonstrates a tongue-like growth pattern similar to low-grade endometrial stromal sarcoma; cells are epithelioid, medium sized with round/oval nuclei, well defined cell borders, abundant granular or clear to eosinophilic cytoplasm, with or without spindle cells; rarely small nests are separated by hyalinized stroma
● Usually no/mild pleomorphism; may have slightly enlarged nuclei with small nucleoli, but relatively smooth nuclear membranes, and evenly dispersed chromatin; may have intranuclear pseudoinclusions
● Variable large, thick-walled vessels
● No mitotic figures, no tumor cell necrosis
● Strong, diffuse cytoplasmic HMB45 expression and focal muscle marker expression
● Group B tumors are composed mainly of diffuse sheets of cells, separately by occasional small, hyalinized bundles and plaques of stroma; contain primarily perivascular epithelioid cells (>50% are round or polygonal) with less prominent, clear features, focal HMB-45 expression, and strong, extensive muscle marker expression
● Possibly malignant features include mitotic activity >1/10 HPF, necrosis, tumor size >5 cm, infiltrative growth pattern, high nuclear grade, cytologic atypia, high cellularity, lymphovascular invasion, infiltration (Adv Anat Pathol 2008;15:63)

Micro images
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Tumors of cervix and endometrium

Positive stains
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● HMB45, SMA (73%), p53 (50%), melanA/Mart1 (24-67%)
● Also calponin, vimentin, h-caldesmon; PR (50%), desmin (49%), muscle-specific actin (36%), ER (33%), CD10 (25%)

Negative stains
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● Chromogranin, p16, EMA, myosin, inhibin, CD56, cytokeratin (positive in 3%), S100 (positive in 3%), CD34 (positive in 5%), CD117 (positive in 9%), and synaptophysin (positive in 17%)

EM description
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● Cytoplasmic myelin figures and marginated nuclear chromatin; no melanosomes

Differential Diagnosis
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● Endometrial stromal sarcoma

Additional References
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● Gynecol Oncol 2003;90:677, Int Semin Surg Oncol 2008 Mar 6;5:7

End of Uterus > Epithelial tumors > Perivascular epithelioid cell tumor (PEComa)

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