At low power, broad nodules of tumor are irregularly pushing into the myometrium.
Another area demonstrates clear infiltration of tumor islands into the myometrium. Note the jagged infiltrative edges. This is the key feature separating a benign endometrial stromal nodule from low grade endometrial stromal sarcoma.
A high power, a dense proliferation of neoplastic stromal cells is seen. By definition, the neoplastic cells must resemble the stromal cells of endometrium (in proliferative phase). They are monotonous small blue cells with round-ovoid nuclei and scant cytplasm.
A different case demonstrates a proliferation of neoplastic stromal cells. An oft-described characteristic feature of endometrial stromal tumors is an arborizing vascular pattern consisting thin-walled branching vessels that may be hyalinized. Although this arborization is difficult to see, a network of delicate vessels can be appreciated in the background.
This case demonstrates another common feature of endometrial stromal tumors. The stromal cells swirl around the thin-walled blood vessels.
This tumor displays some sclerosis, thus appearing almost biphasic. However, these are all neoplastic stromal cells. Note the cells whorling around the blood vessels.
A another case demonstrates short swirling fascicles of neoplastic stromal cells. The cells are monotonous with round to ovoid nuclei, with inconspicuous nucleoli and scant cytoplasm.
Endometrial stromal sarcomas have a proclivity for lymphovascular invasion, as demonstrated by this tumor plug in a vessel. An older name for this tumor was endolymphatic myosis.
Low-grade endometrial stromal sarcomas are histologically identical to benign endometrial stromal nodules with the exception of two key features: infiltration of surrounding myometrium and lymphovascular invasion. The presence of either feature is sufficient to make a diagnosis of low-grade endometrial stromal sarcoma. In the past, mitotic activity was also used to stratify these tumors, but this is no longer the case.
Most endometrial stromal tumors (benign stromal tumors and low-grade stromal sarcomas) demonstrate the same genetic aberration consisting of a translocation t(7;17)(p15;q21) which creates the fusion gene JAZF1-JJAZ1.
Same age distribution as benign endometrial stromal tumors (between 40 and 55 years). Most commonly presents with abnormal uterine bleeding or pelvic pain. 25% of women are asymptomatic. Note that extra-uterine extension into the pelvis is present in 1/3 of cases at the time of diagnosis.1
Hysterectomy and bilateral salpino-oopherectomy is the cornerstone therapy. The ovaries should be removed as these tumors are responsive to hormones and there is a higher risk of recurrence if ovaries are retained. As these tumors contain ER and PR receptors, adjuvant therapy includes aromatase inhibitors as well as radiation for recurrent and metastatic tumors.
Overall 5 year survival rate is 60-80%. These tumors have a propensity for late recurrences. Up to 1/3 of stage I patients develop recurrences, most commonly in the pelvis. The abdomen, vagina and lung have been documented sites of recurrence as well. 'Worm-like' tumor plugs are not uncommonly found in myometrial or parametrial veins.1
1 Nucci MR, Oliva Esther. Gynecologic Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier: 2009: 293-302.
2 Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 667-9.
3 Sternberg SS, ed. Diagnostic Surgical Pathology.4th Ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004: 2497-2501.