Pathologic Diagnosis of Endometrial Stromal Tumors

Tumors composed of cells with features of endometrial stromal cells may be benign or malignant.

Typical endometrial stroma:

(1) cells: blunt, spindled to oblong, with scanty cytoplasm

(2) nuclei: small and uniform

(3) environment: abundant reticulin framework

Feature	Endometrial Stromal Nodule	Low-Grade Endometrial Stromal Sarcoma	High Grade Undifferentiated Uterine Sarcoma
nuclear characteristics	similar to normal stromal cell during proliferative phase; may be enlarged and sometimes show mild atypia	enlarged and may show mild atypia; may be similar to normal stromal cell during proliferative phase	severe nuclear atypia with pleomorphism
mitotic activity	< 10 per 10 HPF	<= 15 per 10 HPF	> 10 per 10 HPF, usually numerous
mitoses	regular	regular	irregular; may be bizarre
margins	pushing	infiltrative	infiltrative
lymphatic and vascular invasion	absent	present; may be seen grossly	present; usually not apparent grossly
invasion beyond uterus	absent	may occur	common

where:

• HPF = high powered field (40x objective lens)

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