Soft tissue sarcoma (STS) is a type of cancer that develops in soft tissues, such as deep skin tissues, muscle, fat, and blood vessels.

STS can occur in any part of the body, including the abdomen.

This article looks at STS in the abdomen, including the symptoms, diagnosis, and outlook for the disease. It also answers some frequently asked questions about STS in the abdomen.

A soft tissue sarcoma in the abdomen.Share on Pinterest
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A person can develop STS in the abdomen.

STS is a malignant cell growth, or tumor, that can occur in soft tissues in the body, such as:

  • nerves
  • skin tissues
  • fat
  • blood vessels
  • fibrous tissues
  • muscle

An individual can develop STS anywhere in the body, although it most often begins in the legs and arms.

People can also develop this type of sarcoma in the internal organs, head, neck, bodily trunk, and retroperitoneum — the back of the abdominal cavity.

Sarcomas are not a common type of tumor. The American Cancer Society (ACS) estimates that doctors will diagnose about 13,400 new STS cases in 2023 and that around 5,140 people may die from STS within the year.

Around 4 in 10 sarcomas start in the abdomen.

There are more than 50 types of STS.

Types of STS that commonly start in the abdomen include:

  • Leiomyosarcoma: This type of cancer starts in smooth muscle tissue, often in the abdomen. It can also begin in other areas of the body, such as in the uterus, legs, or arms.
  • Liposarcoma: This type of tumor occurs in fat tissue and most often starts in the belly, at the back of the abdomen, in the thigh, or in the back of the knee.
  • Desmoplastic small round cell tumor: This is a rare type of sarcoma that mostly occurs in the abdomen in teens and young adults.
  • Undifferentiated pleomorphic sarcoma: While this sarcoma usually begins in the arms or legs, it can also start in the back of the abdomen and can grow and spread to other areas of the body.

Other types of STS include:

  • Clear cell sarcoma: This rare type of soft cell sarcoma typically starts in the tendons of the legs and arms.
  • Adult fibrosarcoma: This type can affect people of all ages and usually develops in the trunk, arms, or legs.
  • Kaposi sarcoma: This type develops in the cells that line blood or lymph vessels.
  • Malignant peripheral nerve sheath tumors: These sarcomas begin in cells that surround nerves. There are several subtypes: neurogenic sarcomas, neurofibrosarcomas, and malignant schwannomas.
  • Angiosarcoma: This type of sarcoma develops in lymph vessels or blood vessels and often affects a part of the body that doctors have treated with radiation.

To diagnose STS, a doctor will typically begin by asking about a person’s medical history and family health history. They will also ask about the symptoms a person has experienced.

A doctor may perform various imaging tests to diagnose STS in the abdomen, including:

  • X-ray: A doctor may perform an X-ray of the abdomen and may then order a specific chest X-ray to check whether the cancer has spread to the lungs.
  • MRI scan: An MRI scan can provide a detailed image of the sarcoma and help doctors determine which soft tissue the tumor has developed in. An MRI uses magnets and radio waves rather than X-rays to provide images of the body.
  • CT scan: If a doctor suspects that a person has an STS in the abdomen, they will typically order a CT scan. This scan provides detailed images of the body and can help doctors determine whether the sarcoma has spread to other areas.
  • Ultrasound: Ultrasounds use sound waves to produce images of the inside of the body. An ultrasound can help a doctor determine whether a lump contains fluid. A solid lump can indicate cancer.
  • PET scan: A PET scan involves a radioactive sugar in the blood that collects in areas where cancer is present.

A doctor may also order a biopsy of the sarcoma. They will remove a small piece of the tumor, which laboratory technicians will examine. This can help a doctor determine whether the tumor is a sarcoma or a benign, or noncancerous, tumor.

The outlook for STS in any area of the body depends on several factors, such as:

  • the type of sarcoma
  • the grade of sarcoma, or how likely it is to spread
  • the stage of sarcoma, or how far it has spread by the time doctors detect it

If doctors detect STS in the abdomen early and it is a low grade tumor that is unlikely to spread, they may be able to cure the sarcoma or remove it through surgery.

A high grade tumor that is larger and in a later stage has a higher risk of spreading or returning after treatment.

It may not be possible for doctors to cure STS if they diagnose it after it has spread to other areas. However, treatments may help manage the symptoms and slow the spread of the cancer.

This section answers some frequently asked questions about STS in the abdomen.

What causes abdominal sarcoma?

Experts do not know the exact cause of STS. Risk factors that experts associate with this cancer include:

  • a family history of cancer
  • exposure to harmful chemicals such as vinyl chloride
  • a damaged lymph system
  • exposure to radiation to treat other cancers

What is a soft tissue mass in abdomen?

STS can affect abdominal soft tissues such as:

  • muscles
  • fat
  • nerves
  • blood vessels
  • fibrous tissue

A mass in any of these soft tissues could indicate STS.

What does abdominal sarcoma feel like?

A person may feel constantly full as a result of swelling in the abdomen and may experience constipation and pain. If the swelling is near the lungs, a person may also feel short of breath or have a persistent cough.

STS is a type of cancer that can affect soft tissues in the body, such as muscle, fat, and blood vessels.

STS can develop anywhere in the body, including in the abdomen. There are more than 50 types of STS, although it is not a common type of cancer.

The outlook for this type of cancer improves significantly with early diagnosis. Doctors may not be able to cure the sarcoma if diagnosis occurs at a later stage of the disease.