The cause of uterine cancer is multifactorial, and these factors can increase your risk of developing this disease. What is known is that something occurs which leads to a genetic mutation within the cells that form the inner lining of the uterus (endometrium) or within the cells that form the uterine muscle. This genetic mutation transforms healthy cells into abnormal cells, which then grow and multiply at an uncontrolled rate and do not die after a normal time span. There can be multiple mutations and some are influenced more by excess estrogen and being overweight than others. The abnormal cancer cells build up into a mass (tumor) and can separate from the uterus to invade other parts of the body (metastasis).