Overview
Leiomyosarcoma (lie-o-my-o-sahr-KOH-muh), also called LMS, is a rare cancer that starts in smooth muscle. Smooth muscle acts by itself and is found in many parts of the body, including the uterus, abdomen, blood vessels, stomach and intestines. LMS is a type of soft tissue sarcoma. Treatment and outlook depend on where the cancer started, its stage and grade, and whether surgery can remove it.
LMS can start almost anywhere in the body where there is smooth muscle, including the uterus, arm, leg or abdomen, also called the retroperitoneum. Some leiomyosarcomas grow quickly and spread to other parts of the body.
Learning you have a rare cancer can bring questions and uncertainty. The outlook for leiomyosarcoma varies from person to person. Several treatment options are available. Your healthcare team can help you understand which options may be right for you.
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Types
Leiomyosarcoma can start in smooth muscle in different parts of the body. The symptoms and treatment can vary depending on where the cancer begins.
- Uterine leiomyosarcoma. Uterine LMS is a cancer that starts in the muscle of the uterus. It is different from a uterine fibroid, also called a leiomyoma. A fibroid is not cancer.
- Leiomyosarcoma of the arms or legs. Leiomyosarcoma can start in smooth muscle in an arm or leg. It may appear as a growing lump. The lump may or may not be painful.
- Retroperitoneal leiomyosarcoma. Leiomyosarcoma can start in the retroperitoneum, the space behind the organs in the abdomen.
- Leiomyosarcoma of the inferior vena cava. Rarely, leiomyosarcoma can start in the inferior vena cava, the large vein that carries blood from the lower body back to the heart.
- Leiomyosarcoma of the stomach or intestines. Rarely, leiomyosarcoma can start in the digestive tract. Tissue testing helps distinguish it from other tumors that can occur there, including gastrointestinal stromal tumors.
Symptoms
Symptoms of leiomyosarcoma depend on where the cancer starts and how large it becomes. Some leiomyosarcomas may not cause symptoms.
Symptoms may include:
- A new or growing lump or swelling.
- Pain or pressure.
- Nausea or vomiting.
- Weight loss without trying.
Symptoms of uterine LMS may include
- Unusual vaginal bleeding.
- Pelvic pain or pressure.
- A lump in the pelvis.
Leiomyosarcoma that starts in an area of the abdomen called the retroperitoneum or in the inferior vena cava may cause belly pain, leg swelling or a mass in the abdomen. The inferior vena cava is the large vein that carries blood from the lower body back to the heart.
Leiomyosarcoma of the arm or leg can appear as a lump. The lump may or may not hurt.
When to see a doctor
Make an appointment with a healthcare professional if you notice a new or growing lump. Make an appointment if you have unexplained pain or swelling that does not go away, or vaginal bleeding that is unusual for you.
If you have been diagnosed with leiomyosarcoma, tell your care team about new or worsening symptoms.
Causes
The cause of leiomyosarcoma is not clear.
Leiomyosarcoma begins when changes happen in the DNA of a smooth muscle cell. DNA contains the instructions that tell a cell what to do. The changes tell the cell to grow and multiply when other cells would die. The extra cells can form a tumor.
Cancer cells can break away from the tumor and spread to other parts of the body. Cancer that spreads is called metastatic cancer.
Risk factors
Factors that may raise the risk of leiomyosarcoma include:
- Certain inherited cancer syndromes and gene changes. Examples include Li-Fraumeni syndrome, which can be caused by a change in the TP53 gene, and hereditary retinoblastoma, which can be caused by a change in the RB1 gene. These genes normally help control how cells grow and divide. Researchers are still studying inherited risk.
- Radiation therapy in the past. Rarely, LMS can develop many years after radiation therapy for another condition.
Talk with your healthcare team if you have questions about how your personal or family medical history may affect your risk.
Complications
Leiomyosarcoma can:
- Spread to other parts of the body. The lungs are a common place for LMS to spread. The liver and other areas also can be affected.
- Affect how nearby organs or blood vessels work as a tumor grows.
LMS can be a serious cancer because some tumors grow quickly or spread. But the course of the cancer varies from person to person.
Aug. 29, 2026