A 38-year-old woman complains to her physician of chronic pelvic pain that is much worse during her menstrual periods. Pelvic examination demonstrates an enlarged uterus with multiple palpable masses. Ultrasound shows that a large number of ball-like masses up to 6 cm diameter are present in the uterus. Which of the following is the most likely cause of the ball-like masses in her uterus?

Leiomyomas are benign ball-like masses that commonly form in the uterus. Cervical and uterine carcinomas tend to initially form a fairly superficial layer of cancer on the surface of the endocervix or uterine cavity, which may later become deeply infiltrative. Usually, no ball-like mass is produced. Leiomyosarcomas are very rare tumors, which form masses that are usually less regular in geometry than leiomyomas.