DESCRIPTION

• A tumor that forms in the connective tissues, such as tendons, muscles, ligaments, cartilage, nerves, or fat
• Soft tissue masses classically present as a painless growing soft-tissue lump or bump. They can be firm or soft. They can be observed by physical exam or radiographically.
• Most soft tissue masses are benign, but a small minority are malignant and require intensive multimodal therapy.

EPIDEMIOLOGY

• It is difficult to estimate the incidence of benign soft tissue masses. Many are diagnosed on physical exam or radiologically and never biopsied.
• Malignant soft tissue tumors, or soft tissue sarcomas, account for approximately 20% of all pediatric malignant cancers.
• There are approximately 900 new cases of rhabdomyosarcoma (RMS) and non-RMS soft tissue sarcomas (NRSTS) each year. RMS is the most common soft tissue sarcoma in children ≤14 years, and NRSTS is more common in adolescents and young adults.

COMMONLY ASSOCIATED CONDITIONS

There have been associations between trauma and soft tissue masses, but trauma is not the culprit, and it was likely the trauma that drew medical attention to the already existing mass. An exception is a ganglion cyst, a benign fluid-filled soft tissue mass caused by injury. However, there are some disorders that are associated with soft tissue lesions.

• Malignant peripheral nerve sheath tumors are associated with neurofibromatosis.
• RMSs are associated with Li-Fraumeni syndrome and hereditary retinoblastoma.
• Desmoid tumors are associated with Garner syndrome.
• Leiomyosarcomas are associated with Li-Fraumeni syndrome.
• Kaposi sarcoma is associated with HIV or human herpesvirus (HHV)-7.
• Epstein-Barr virus is associated with smooth muscle tumors in patients with immunodeficiency.

HISTORY

• History of trauma—many soft tissue lesions are found incidentally.
• Pain—most soft tissue tumors are painless and do not cause limb dysfunction. However, depending on the location, it may cause pain or neurologic symptomatology.
• Rate of growth—rapid growth raises the suspicion for malignancy.
• Family history—a detailed family history assessing for cancer risk is obligatory in all evaluations of soft tissue masses.

PHYSICAL EXAM

• Musculoskeletal findings—location and size of the lesion or lesions should be assessed and measured; look for joint involvement, range of motion; assess for signs/symptoms of neurovascular compromise.
• Lymph node involvement—regional lymph nodes should always be examined.
• Skin findings
  • Café au lait spots and neurofibromas are associated with neurofibromatosis.
  • Erythema, warmth, and tenderness suggest infection and an inflammatory process.

DIFFERENTIAL DIAGNOSIS

• Benign:
  • Arteriovenous malformation
  • Baker cyst
  • Desmoid tumor
  • Epidermal cyst
  • Ganglion cyst
  • Giant cell tumor
  • Hemangioma
  • Leiomyoma
  • Lipoma
  • Myoma
  • Neuroma
  • Neurofibroma
  • Nodular fasciitis
  • Schwannoma
  • Solitary fibrous tumor
• Malignant:
  • Alveolar soft part sarcoma
  • Clear cell sarcoma
  • Chondrosarcoma
  • Dermatofibroma protuberans
  • Desmoplastic small round cell tumor
  • Ewing sarcoma
  • Extraskeletal myxoid chondrosarcoma
  • Fibrosarcoma
  • Kaposi sarcoma
  • Leiomyosarcoma
  • Malignant fibrous histiosarcoma
  • Malignant hemangiopericytoma
  • Malignant peripheral nerve sheath tumor
  • Myxoid liposarcoma
  • Pleomorphic sarcoma
  • RMS
  • Synovial sarcoma
• Other
  • Autoimmune disease
  • Langerhans cell histiocytosis
  • Osteomyelitis

DIAGNOSTIC TESTS & INTERPRETATION

There are no definitive tests that will help differentiate soft tissue masses. In patients with NRSTS, a baseline complete blood count (CBC) count with differential is useful in evaluating for involvement of bone marrow.

MEDICATION

• Systemic chemotherapy is typically reserved for aggressive or malignant soft tissue lesions. Common regimen used is ifosfamide and doxorubicin.
• Targeted therapies, depending on the diagnosis, may be used (e.g., Larotrectinib, a neutrophil tropomyosin receptor kinase [NTRK] inhibitor, for infantile fibrosarcoma [characterized by NTRK mutations]).

ISSUES FOR REFERRAL

Most patients should be referred to medical centers with specialists who have expertise in diagnosing and treating soft tissue lesions.

SURGERY/OTHER PROCEDURES

• Complete local excision is adequate treatment for benign soft-tissue tumors.
• Variety of treatment options, including surgery alone or combined with radiation therapy and/or chemotherapy, may be considered for treatment of localized primary and recurrent sarcomas.

ADMISSION, INPATIENT, AND NURSING CONSIDERATIONS

• Most patients with newly diagnosed soft tissue masses start the workup and may even be completely managed as an outpatient.
• For patients with significant pain, admission is recommended for pain control and to expedite diagnosis and therapy.
• If there are signs of neurovascular compromise, urgent admission with consultation by orthopedics, neurology, neurosurgery, or vascular surgery is recommended.
• Pediatric oncology consultation may be considered based on the index of suspicion for a malignant soft tissue tumor. Surgical subspecialists should be consulted based on the location of the tumor.

FOLLOW-UP RECOMMENDATIONS

• Close follow-up and repeated imaging are important with varying time intervals depending on the lesion.
• Patients with malignant soft tissue tumors will require vigorous surveillance for 5 years posttreatment.

PROGNOSIS

Most soft tissue masses seen in children are benign, and their prognosis is excellent. Some lesions do not require intervention. Surgery, if needed, is curative for most benign lesions.

COMPLICATIONS

• Pain
• Restrictions in movement
• Infection
• Wound dehiscence
• Pathologic fracture