Ultimately, the uterus should shrink up after menopause, and bleeding from it should totally cease. As you can see from the way the uterus' inner lining cycles between thickening and getting sloughed off, there are new cells forming in the uterus followed by cell death. It is a very dynamic system. Normally, the formation of new cells, from the division of previous ones, is a very tightly controlled process. In the fertile woman, this control is by the female hormones estrogen and progesterone.
Uterine cancer starts in just one cell.
A change occurs in this cell which causes it to lose control of it's division, and so it starts dividing in an uncontrolled manner. Most swellings in the uterus aren't malignant, but when they are, they will spread if untreated and eventually kill the patient. Uterine cancer is the most common gynecological cancer in American women, with 35,000 new cases each year. It causes 3000 deaths each year. You can see that less than one woman in ten dies of their disease.