Uterine tumour. Light micrograph of a section through an angioleiomyoma from a female patient's uterus. Leiomyomas are benign (non-cancerous) tumours that are found in smooth muscle. They are most common in the uterus, small bowel and oesophagus. Angioleiomyomas (or vascular leiomyomas) are thought to arise from the smooth muscle of blood vessels.