The American Cancer Society describes uterine sarcoma as cancer that starts in the muscle and tissues that support the uterus. This differs from endometrial cancer, which starts in the lining of the uterus called the endometrium.

The endometrium is the lining of the uterus, and on imaging tests like ultrasounds, the lining is referred to as the endometrial stripe, according to the gynecologic oncologist Dr. Kate O'Hanlan.