One of the rarest types of uterine cancer is endometrial stromal sarcoma (ESS), a uterine cancer that accounts for less than 1 percent of cancers of the reproductive organs.

"'Normal' endometrial cancer develops from the glands, whereas endometrial stromal sarcoma develops from a different type of cell," says Karen Lu, MD, a professor of gynecologic oncology at the University of Texas M. D. Anderson Cancer Center in Houston. "It's a much more rare type, but in general they tend to be less aggressive. It can be managed with either surgery or hormone therapy."

ESS tends to occur in women who are younger than the average age for uterine cancer in general. While the common type of uterine cancer usually occurs in women who are past menopause , ESS is more often seen in premenopausal women in their 40s to 50s.

ESS can be low-grade (LGESS), which tends to be slow-growing, or high-grade (sometimes known as undifferentiated ESS), which may grow more quickly.