[Rectal leiomyosarcoma, a rare malignant tumor diagnosed in ulcerative colitis].

Patients with chronic inflammatory diseases (IBD) of the digestive tract are known to have an increased risk of colorectal cancer. These are usually adenocarcinomas, and the occurrence of malignant mesenchymal tumours, particularly leiomyosarcomas, is exceptional. We report one case in a 40-year-old woman, followed for 9 years for ulcerative colitis. The tumour measured 2cm in length and infiltrated the entire rectal wall as far as the subserosa. It was composed of fusiform cells, with 5 mitoses for 10 fields at ×400 magnification, and expressing actin, desmin and caldesmone under immunohistochemical study. We review the 2 cases of leiomyosarcomas associated with Crohn's disease and 3 cases developed during ulcerative colitis published in the literature.