Epithelial refers to the surface lining, and ovarian refers to ovary, of which women have two that sit along either side of the uterus so epithelial ovarian cancer, is a cancer that forms along the surface of an ovary.
Now, each ovary contains multiple follicles.
And, each follicle is made up of a germ cell, also known as an oocyte, which is the immature egg.
Between the follicles is the stromal or connective tissue cells, and lining the ovary is a layer of epithelial cells.
Ovarian tumors are generally grouped based on these three types of cells in the ovaries, and the majority of ovarian cancers are epithelial kind.
Now, if an epithelial cell starts to divide uncontrollably, it can either be a benign tumor which means that it does not invade nearby tissue or spread to other parts of the body, or it can be a malignant tumor which means that it might invade or spread to other tissues.
Compared with benign tumor cells, a distinguishing feature of malignant tumor cells have slightly less organized nuclei.
A third class of tumors are called borderline tumors because they have features that are intermediate between the other benign and malignant tumors.
Epithelial ovarian cancers can be subdivided into four types: serous, mucinous, endometrioid and transitional.
Serous and mucinous tumors arise from epithelial cells that line the outside of ovaries, whereas even though the tumors are found in the epithelium, the endometrioid and transitional cell tumors arise from other cell types.
Serous tumors have fluid-filled cysts, typically a single cyst, and can be benign, malignant, or borderline.
Benign serous tumors are called serous cystadenomas, and are the most common type, and often develop on both ovaries, and typically affect premenopausal women.
Mucinous tumors, on the other hand, have mucus-filled cysts that often involve large multiloculated cysts, but can also be benign, malignant, or borderline.
