Endometrioid tumor

Endometrioid tumors are a class of tumors that arise in the uterus or ovaries that resemble endometrial glands on histology. They account for 80% of endometrial carcinomas and 20% of malignant ovarian tumors.

Ovary

Ovarian endometrioid tumors are part of the surface epithelial tumor group of ovarian neoplasms.
Benign and borderline variants are rare, as the majority are malignant.
There is an association with endometriosis and concurrent primary endometrial carcinoma.
On gross pathological examination, the tumor is cystic and may be solid and some arise in cystic endometriosis. In 40% of cases, endometrioid tumors are found bilaterally.

Endometrium

Endometrioid carcinoma can also arise in the endometrium.
Grades 1 and 2 are considered "type 1" endometrial cancer, while grade 3 is considered "type 2".

Light microscopy

Light microscopy shows tubular glands, resembling endometrium.

Molecular biology

CTNNB1 and PTEN mutations

Ovarian and endometrial endometrioid carcinomas have distinct CTNNB1 and PTEN gene mutation profiles. PTEN mutations are more frequent in low-grade endometrial endometrioid carcinomas compared with low-grade ovarian endometrioid carcinomas. By contrast, CTNNB1 mutations are significantly different in low-grade ovarian endometrioid carcinomas compared with low-grade endometrial endometrioid carcinomas. This difference in CTNNB1 mutation frequency may be reflective of the distinct tumoral microenvironments; the epithelial cells lining an endometriotic cyst within the ovary are exposed to a highly oxidative environment that promotes tumorigenesis.