About 1 in 100,000 people gets diagnosed with LMS each year. Leiomyosarcoma is one of the more common types of soft-tissue sarcoma, representing 10 percent to 20 percent of new cases. Leiomyosarcomas can be very unpredictable. They can remain dormant for long periods of time and recur after years. The cancer is aggressive and hardly responds to chemotherapy treatments.