Endometrial stromal sarcoma
Micrograph of a low-grade endometrial stromal sarcoma. H&E stain.
Specialty	Oncology, gynecology

Endometrial stromal sarcoma is a malignant subtype of endometrial stromal tumor arising from the stroma (connective tissue) of the endometrium rather than the glands. There are three grades for endometrial stromal tumors, as follows.^[1] It was previously known as endolymphatic stromal myosis because of diffuse infiltration of myometrial tissue or the invasion of lymphatic channels.^[2]

Low-grade endometrial stromal sarcoma

Low-grade endometrial stromal sarcoma consists of cells resembling normal proliferative phase endometrium, but with infiltration or vascular invasion. These behave less^[3] aggressively, sometimes metastasizing, with cancer stage the best predictor of survival. The cells express estrogen/progesterone-receptors.

Undifferentiated uterine sarcoma

Undifferentiated uterine sarcoma, or undifferentiated (high-grade) endometrial stromal sarcoma, does not resemble normal endometrial stroma and behaves much more aggressively, frequently metastasizing. The differential includes leukemia, lymphoma, high-grade carcinoma, carcinosarcoma, and differentiated pure sarcomas.

Pathology

Macroscopy

• Polypoid mass extending into broad ligament, ovaries and fallopian tubes.
• Lymphatic tumor plugs as yellow, ropy or ball-like masses.

Microscopy

• Monotonous ovoid cells to spindly cells with minimal cytoplasm.
• Prominent arterioles. Angiolymphatic invasion common.
• Up to 10-15 mitotic figures per 10 HPF in most active areas.
• Tongue-like infiltration between muscle bundles of myometrium.
• May exhibit myxoid, epithelioid and fibrous change.
• May have foam cells or hyalinization in the stroma.

Immunochemistry

• CD10+
• muscle markers (muscle specific actin MSA, smooth muscle actin SMA and desmin) positive in areas of smooth muscle differentiation
• CD117- (c-kit -)
• h-caldesmon-

Genetic features

A recurrent chromosomal translocation, t(7;17)(p15;q21), occurs in endometrial stromal sarcoma. This translocation leads to the fusion of two polycomb group genes, JAZF1 and JJAZ1, with production of a fusion transcript with anti-apoptotic properties. Even normal endometrial stroma cells express the fusion gene, derived not by translocation, but by the "stitching" together of m-RNAs. Thus, it appears that a pro-survival gene in the normal endometrium is somehow subverted to become pro-neoplastic.^[4]