Lumps and bumps are common in childhood, but when they form in soft tissue without an obvious cause, they could be pediatric soft tissue sarcoma (STS).

In children, cancer that forms in the soft connective and supportive tissues of the body is known as pediatric STS. Although relatively rare, it is a type of cancer that accounts for up to 7% of all childhood tumors.

With more than 50 subtypes of STS, a diagnosis can come with a wide variety of presentations, treatments, and outcomes.

This article outlines pediatric STS, including its symptoms, diagnosis, and treatment.

A young person with pediatric soft tissue sarcoma riding in a car.Share on Pinterest
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Sarcoma is a general term used for various solid, cancerous tumors originating from mesenchymal cells in the bone or soft tissues. They are different from carcinomas, which originate in epithelial cells of the skin and organs.

Pediatric STS can form anywhere in the soft tissues of the body, including:

  • muscles
  • nerves
  • tendons
  • blood vessels
  • lymph nodes
  • fat
  • joint tissues

While there are more than 50 subtypes of STS, doctors typically divide pediatric tumors of this class into two groups:

  • rhabdomyosarcoma (RMS)
  • nonrhabdomyomatous STS (NRSTS)

RMS accounts for approximately 4% of all childhood tumors and 50% of STS between the ages of 0 and 14. It is a tumor that forms in skeletal muscle.

Types of RMS include:

  • embryonal
  • alveolar
  • pleomorphic
  • spindle/sclerosing

NRSTS makes up another estimated 3.5% of childhood tumors. Doctors often classify NRSTS based on the tissue it originates from.

Types of NRSTS include:

Read about STS prevalence here.

A small, painless lump is the most common symptom of pediatric STS. As the tumor grows and creates pressure, it may start to cause discomfort, weakness, or impaired function.

Common locations are in the extremities, chest, and abdomen.

Additional symptoms may occur based on the area of the body affected. For example, an STS that presses on the bladder may cause blood in the urine.

Whole-body symptoms, such as weight loss or fever, are rare but possible.

There are many conditions that can cause a lump in the soft tissue. Proper diagnosis involves a physical examination and medical history to help determine the likelihood of pediatric STS.

Diagnostic imaging helps identify the tissues affected. This may include the use of:

Blood testing can also be beneficial to establish baseline values and assess organ function, but there is currently no specific blood test that can indicate a pediatric STS.

If diagnostic testing indicates a potential tumor, the next step is a biopsy of the site.

A doctor can perform a biopsy in a variety of ways depending on the tumor’s location. A biopsy involves removing a tissue sample or the entire lump, in some instances, for type verification by a pathologist.

Doctors may also take tissue samples from adjacent sites or other areas to determine whether cancer cells have metastasized, or spread.

Once a pathologist has diagnosed soft tissue sarcoma and the type of tumor, doctors can design an individual treatment plan.

The American Joint Committee on Cancer (AJCC) created the TNM system to stage all cancers, including STS. It uses the following letters to indicate details about the tumor:

  • T: the size/extent of the tumor
  • N: the degree of spread to nearby lymph nodes
  • M: whether cancer has metastasized or spread
  • G: the grade of the cancer cells

Staging is dependent on where the cancer is in the body. Once doctors have determined the tumor location and the TMN score, overall staging falls into six final categories:

  • 1A: small tumors, no lymph node involvement, no metastasizing, low grade
  • 1B: medium to large tumors, no lymph node involvement, no metastasizing, low grade
  • 2A: small tumors, no lymph node involvement, no metastasizing, grade 2 or 3
  • 3A: medium tumor size, no lymph node involvement, no metastasizing, grade 2 or 3
  • 3B: medium to large tumor size, possible lymph node involvement, no metastasizing, grade 2 or higher
  • 4: tumor of any size or grade that has spread to lymph nodes, possibly metastasizing

A higher staging indicates a more advanced cancer. Depending on the location of the STS, the criteria for stages 3B and 4 can vary.

An oncologist, a doctor who specializes in cancer, leads pediatric STS treatment, but many other specialists may be involved.

Treatment approaches for pediatric STS include:

  • Surgery: Surgeons remove the affected tissue.
  • Radiation therapy: Doctors use radiation to kill cancer cells.
  • Chemotherapy: This involves using chemotherapy medications to kill or slow cancer cells.
  • Immunotherapy: Immunotherapy involves using substances to boost the body’s natural immune response to cancer.
  • Targeted therapy: This involves administering substances that target specific cancer cells only.
  • Other drug therapy: This may include medications, such as steroids, hormones, or analgesics.
  • Observation: Doctors may recommend this when other therapies are not possible or cancer is not affecting vital organs.

Treatment varies and depends on numerous factors. For example, some children may only need tumor removal surgery while other children may require amputation of affected limbs.

Collectively, the 5-year survival rate for pediatric STS is over 70%. However, the wide presentation of these tumors affects the overall prognosis.

Factors that can affect outcomes include:

  • whether doctors can surgically remove the cancer
  • tumor location and depth
  • cancer grade
  • presence of metastasization
  • potential for radiation therapy

Generally, tumors that surgeons can remove are associated with the best 5-year survival rates. It is possible for treatment to completely eliminate STS in some people.

Learn about the outlook for STS here.

Pediatric soft tissue sarcoma is a rare type of cancer affecting the soft, supportive tissues of the body. It accounts for approximately 7% of pediatric tumors.

The most common symptom of STS is a small, painless lump, commonly in the extremities, chest, or abdomen.

Surgical removal is associated with the best outcomes and the highest chances of eliminating the cancer.

Overall, 5-year survival rates for this cancer are above 70%.