Here is some info I have compiled from surfing the web.
"Leiomyosarcoma (LMS) is a rare cancer, part of a family of cancers known as sarcomas. Sarcomas are cancers that arise in the body's connective tissues, which include fat, muscle, blood vessels, deep skin tissues, bones and cartilage. Sarcomas are either soft tissue tumors or bone tumors." (1)
Leiomyosarcoma "is an extremely rare type of cancer; in the Unites States, for example, the frequency of leiomyosarcomas is just 1.4 cases per 100,000 people." (2)
Sources:
1: http://www.leiomyosarcoma.info/images/pamphlet2col.pdf
2: http://www.wisegeek.com/what-is-leiomyosarcoma.htm
