These tumours originate in smooth muscle cells. Smooth muscles are found in various organs and tissues throughout the body, such as the uterus, gastrointestinal tract, blood vessels, and walls of organs like the bladder and prostate. Leiomyosarcoma can occur in any of these locations, but the most common sites include the uterus (known as uterine leiomyosarcoma) and the gastrointestinal tract. ​

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 Leiomyosarcomas are aggressive tumours and can vary in their behaviour and prognosis depending on factors such as tumour size, location, grade, and stage. They often grow and spread silently, with symptoms usually manifesting in the later stages.