Leiomyoma Leiomyomas are smooth muscle tumour that are mostly benign. 1/1000 becomes cancer. The most likely sites are esophagus, stomach, small intestine and uterus, but they can occur in any organ. They are the most common benign mesenchymal tumour of the esophagus. The most common mesenchymal tumour of the small intestine and stomach is a ..