Surface epithelial-stromal tumor
Surface epithelial-stromal tumors are a class of ovarian neoplasms that may be benign or malignant. Neoplasms in this group are thought to be derived from the ovarian surface epithelium (modified peritoneum) or from ectopic endometrial or fallopian tube (tubal) tissue.
Source: Wikipedia — Surface epithelial-stromal tumor (CC BY-SA 4.0)