October 2015 Case of the Month

42 year-old woman with a 24 cm pelvic mass focally adherent to small bowel, status post hysterectomy and partial small bowel resection.  Grossly, the tumor appeared to extended from an endometrial polyp transmurally through the myometrium, with the majority of tumor represented as a large exophytic mass protruding from the uterine surface.  Periadnexal nodules were also noted.

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2x

The uterine tumor displays hypercellular appearance on low power with nodular and nested architectural pattern. The tumor nests infiltrate into the myometrial smooth muscle.

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10x
10x

Scattered small vessels are noted in a background of monotonous tumor cells.

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Desmin immunostain 40x
Desmin immunostain 40x

Negative

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2x

The uterine tumor displays hypercellular appearance on low power with nodular and nested architectural pattern. The tumor nests infiltrate into the myometrial smooth muscle.

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October 2015 Case of the Month

   Answer: Low-Grade Endometrial Stromal Sarcoma

The hysterectomy specimen demonstrates a large hypercellular tumor comprised mostly of crowded monotonous cells.  The neoplastic cells are relatively uniform in appearance without significant pleomorphism.  Mitotic activity is low.  Characteristically, the tumor shows extension from a polypoid endometrial mass through the myometrium, admixed foamy histiocytes, and frequent worm-like plugs of tumor within dilated parametrial and adnexal vessels.  By immunohistochemistry, the tumor is CD10 positive and desmin negative.  These features are all characteristic of an endometrial stromal sarcoma (ESS).  ESS accounts for roughly 10-15% of mesenchymal uterine cancers, and the majority occur in patients less than 50 years of age.  These tumors tend to behave in a more indolent manner, with mainly a propensity for local recurrence, sometimes years after hysterectomy.  Nodal metastasis and hematogenous spread is a rare occurence.  In this case, despite the adherent small bowel and omentum, the tumor did not invade other organs or show nodal spread.  The tumor was ER and PR positive which may have potential therapeutic significance.