Case History

A 48-year-old woman underwent a hysterectomy for a uterine mass. The neoplastic cells stained positive for CD10, ER, SMA, focal cyclin D1, and negative for desmin, caldesmon, STST6, SF1, and HMB-45. Sarcoma fusion panel showed JAZF1-SUZ12 fusion.

What is the correct diagnosis?

A. High-grade endometrial stromal sarcoma
B. Endometrial stromal nodule
C. Low-grade endometrial stromal sarcoma
D. Smooth muscle tumor of uncertain malignant potential (STUMP)

 5.2.22 Case 1 Photo

5.2.22 Case 2

Answer C: Low-grade endometrial stromal sarcoma

Low-grade endometrial stromal sarcoma is a malignant stromal tumor with cells resembling proliferative phase endometrial stroma and displaying infiltrative growth with or without lymphovascular invasion.

Histologically, the tumor has irregular, densely cellular islands of tumor cells with a diffuse growth permeate the myometrium and maybe associated with lymphovascular invasion.

Cells have uniform, oval to fusiform nuclei with no or minimal atypia, scant cytoplasm and delicate arteriolar network. Mitotic activity is usually low but can be brisk. Smooth muscle differentiation, sex-cord differentiation and fibromyxoid/fibrous change are common.

The tumors usually show strong expression of CD10, ER, PR and focal cyclin D1, keratins,

Top differential diagnosis include endometrial stromal nodule and high-grade endometrial stromal sarcoma. The most important factor to differentiate endometrial stromal nodule from low grade endometrial stromal sarcoma in myometrial infiltration. Endometrial stromal nodule is well circumscribed and the junction of nodule to myometrium should be extensively sampled to rule out sarcoma. High-grade endometrial stromal sarcoma may show more than one pattern of infiltration. The ones harboring ZC3H7B-BCOR fusion show strong diffuse expression of cyclin D1. They typically show diffuse CD10 positivity and variable ER and PR positivity. The ones with BCOR internal tandem duplication (BCOR ITD) are less positive for CD10, diffusely positive for cyclin D1 and negative for ER and PR.

Low grade endometrial stromal sarcoma is a relatively indolent sarcoma, with protracted clinical course even in patients with recurrent disease. Stage is the most important prognostic factor.

Selected references:

1. Low-grade endometrial stromal sarcoma, WHO Classification of Tumors, Female Genital Tumors 5TH edition.

Case contributed by: Mariam Youssef, M.D., Breast/GYN Fellow, UAB Pathology