A soft tissue sarcoma (STS) is a malignant tumor that starts in soft tissue such as muscle, deep skin tissues, cartilage, or fat. It might feel like a lump in the arm muscle area. People can develop STS in any body part, including the arms.

Most cases of STS first develop in the arms or the legs.

This article discusses the types and symptoms of soft tissue sarcoma in the arm, diagnosis, outlook, and more.

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STS mostly begins in the arms and legs, but a person can develop the condition in any soft tissue in the body, which includes:

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

As well as in the arms and legs, people commonly develop sarcomas in areas such as:

  • the trunk
  • neck
  • head
  • internal organs
  • abdomen

There are several types of STS, and some are more common in particular areas of the body. Types that people commonly develop in the arm are as follows:

  • Adult fibrosarcoma: This is a rare and aggressive type of STS, which doctors can find challenging to treat. It usually begins in connecting tissues called fascia or tendons in the arms, legs, or trunk. This type of soft tissue sarcoma can affect people of any age, although it most commonly develops in people between 30 and 60 years.
  • Clear cell sarcoma: This is a rare type of cancer that typically develops in the tendons of the arms or legs. This type of sarcoma can affect people of all ages, but most commonly it develops in adults around the age of 39 years.
  • Low grade fibromyxoid sarcoma: People sometimes refer to this as Evan’s tumor — it typically grows slowly and presents as a painless growth in the arms, legs, or trunk. This type of tumor is most common in adults in their 30s.
  • Low grade myxofibrosarcomas: These tumors typically develop under the skin’s surface in the arms and legs. They usually affect older people and can present with multiple tumors.
  • Leiomyosarcoma: These tumors develop in smooth muscle tissue, typically in the abdomen, although they can start in the arms, legs, and uterus.
  • Undifferentiated pleomorphic sarcoma: An aggressive type of soft tissue sarcoma that typically starts in the arms or legs, usually in older adults. It can grow rapidly and metastasize to distant areas of the body.
  • Solitary fibrous tumors: They typically do not spread to other parts of the body. They can be malignant but are often benign, and usually start in the underarm, thigh, or pelvis.

STS can develop in flexible tissue and can move and stretch regular tissue out of the way as they grow.

This means people typically do not experience symptoms of STS in the early stages, and tumors can grow for some time before they cause issues.

The most common sign of soft tissue sarcoma in the arm is a lump or area of swelling. The lump may be painless or cause pain if the sarcoma presses against nerves or muscles.

Medical professionals commonly find these lumps to be lipomas — noncancerous tumors of the fat cells that are typically harmless. Sometimes, they find them to be sarcomas, which are cancerous growths.

However, a person should contact a doctor if they notice new lumps to rule out cancer or other serious causes.

It may be easier to treat STS in the arm than in the trunk, chest, or head. This is because it may be easier to surgically remove the sarcoma when it is in the leg or the arm.

Previously, doctors would commonly treat sarcomas in the arm by removing the limb. Today, there is less need, as surgeons can perform limb-sparing surgery.

For this, they may use an implant or tissue graft to replace any tissue they remove.

After surgery, they may use radiation therapy to reduce the sarcoma even further. Other treatments include chemotherapy and targeted therapy.

The outlook for STS in the arm can vary depending on several factors, including:

  • the type of sarcoma a person has
  • whether the sarcoma has spread to other areas of the body
  • an individual’s age and overall health

According to the American Cancer Society, there is an overall 65% 5-year relative survival rate for STS for all stages combined.

This means that people with STS are 65% as likely as the general population to live for at least 5 years after diagnosis.

Survival rates for specific stages of STS are as follows:

SEER stage Stage description 5-year relative survival rate
Localized STS is limited to the area where it first developed and has not spread to other tissues. 81%
Regional STS has spread to nearby lymph nodes or structures.56%
Distant STS has spread to other organs or structures. 15%

This section answers common questions about soft tissue sarcoma in the arm.

What does sarcoma in the arm feel like?

A lump from STS in the arm may be painless but could cause pain if the tumor presses against nerves or muscles.

A person generally cannot move the lump around easily.

How common is arm sarcoma?

Around 15% of soft tissue sarcomas occur in the arms. People more commonly develop STS in the lower extremities of the body.

STS is a rare type of cancer that develops in the soft tissues of the body, such as in the muscle, fat, or blood vessels.

STS can occur in any area of the body, although some types more commonly develop in the arms and legs than other types.

The most common symptom of STS in the arm is a lump, which may be painful or painless, depending on whether it is pressing against nerves or muscles.

The outlook is better for people whose sarcoma has not spread to other areas of the body.