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 GIST (gastrointestinal stromal tumour), but leiomyomas come in second. Mesenchymal neoplasms of the gallbladder are rare, especially leiomyomas, almost always in combination with an immune deficiency. Leiomyomas can result in in an increased erythropoietin production leading to polycythemia.
Leiomyosarcomas are malignant smooth muscle tumours. It is thought they do not arise from leiomyomas, but leiomyomas can become malignant too, although this is very rare (0,1%). The most common sites are uterus, stomach, small intestine and retroperitoneum. The incidence of leiomyosarcomas is 1 in 100,000. The disease course of leiomyosarcomas can vary over time, being silent for long periods before accelerating in growth. They are resistant to chemotherapy or radiation, so early surgery is the best option.
Leiomoysarcomas in the duodenum can have central ulceration or fistula formation. Leiomyosarcomas often invade extraluminal space.
Leiomyosarcomas are well-differentiated or poorly-differentiated. They have a high mitotic rate. Poorly-differentiated there is also atypia. Leiomyomas have a low mitotic rate. DOG1 is negative (GIST tumours) Desmin, Smooth actin and Caldesom are mostly positive in both leiomyomas and leiomyosarcomas. Ki67 is low in Leiomyomas (mitosis). There is no immuno-histochemical marker that can differentiate between a leiomyoma and leiomyosarcoma.
Carvalho JC, Thomas DG, Lucas DR. Cluster analysis of immunohistochemical markers in leiomyosarcoma delineates specific anatomic and gender subgroups. Cancer. 2009;115(18):4186‐4195. doi:10.1002/cncr.24486