The endometrium is a mucous membrane, well supplied with blood vessels, that lines the uterus (the small, hollow, pear-shaped organ in a woman's pelvis in which a fetus develops). It becomes thickened in the latter part of the menstrual cycle, but if no pregnancy occurs it is shed during menstruation.
Endometrial cancer is cancer that forms in the endometrium. Most endometrial cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).
For further information see cancer of the uterus.