Soft tissue sarcoma (STS) is a rare cancer that develops in the body’s connective tissues, such as fat, muscle, nerves, and blood vessels. These tumors can appear in almost any part of the body, but they are most often found in the arms and legs. Because STS appearance is highly variable and often mimics benign lumps, a visual assessment alone cannot determine if a mass is cancerous. The presence of a new or growing lump should always be evaluated by a healthcare professional, as only imaging and a biopsy can confirm a diagnosis.
Key Physical Characteristics of Soft Tissue Sarcoma
The initial physical characteristic of a soft tissue sarcoma is usually an unexplained mass or lump beneath the skin surface. This mass may be completely painless at first, which can lead many people to ignore it until it has grown substantially. The skin over the lump is typically unaffected, meaning there is no change in color or texture.
When felt, a suspicious mass often has a distinct texture and mobility compared to common benign growths like lipomas. Sarcomas are described as feeling firm, solid, or rubbery to the touch. They are often fixed or tethered to the surrounding deep tissue layers, unlike a benign lipoma which is easily moveable beneath the skin.
Soft tissue sarcomas are frequently deep-seated, meaning they originate beneath the fascia, a layer of connective tissue covering the muscles. By the time they are noticed, these tumors are often larger than five centimeters, roughly the size of a golf ball. A mass that is deep to the fascia or that has reached this size is a significant indicator that a thorough medical investigation is warranted.
Common Anatomical Sites
Soft tissue sarcomas can arise from any mesenchymal tissue, but certain locations are far more common than others. Approximately 60% of all cases occur in the extremities, with the lower limbs affected more often than the upper limbs. The thigh is the single most common site for these tumors to develop.
The trunk, including the chest, back, and shoulders, is another frequent location for STS. About 20% of soft tissue sarcomas are found in the retroperitoneum, the space behind the abdominal cavity. Sarcomas in this internal location can grow quite large before they are noticed, as they do not create a visible external lump.
Growth Rate and Associated Symptoms
A key feature distinguishing a soft tissue sarcoma from a benign lump is its growth pattern. While many benign masses remain stable or grow slowly over years, a sarcoma typically demonstrates continuous and progressive enlargement over weeks or months. Any mass that is noticeably increasing in size over a short period requires urgent medical attention.
As the tumor grows, it may begin to press on adjacent nerves, blood vessels, or muscle compartments, leading to new or worsening symptoms. This pressure can cause a persistent, localized pain that does not resolve with rest or typical pain medication. If the mass is pressing on a nerve, a person may experience numbness, tingling, or weakness in the affected limb.
Sarcomas located in an extremity can cause swelling or edema distal to the mass due to compression of blood or lymph vessels. For tumors in the abdomen, symptoms often relate to pressure on internal organs, such as persistent belly pain, a feeling of fullness after eating, or changes in bowel or bladder function. These symptoms indicate a growing mass is interfering with normal function.
When to Consult a Specialist
Because the initial appearance of a soft tissue sarcoma is non-specific, several “red flags” should prompt immediate consultation and referral to a specialist. Any lump that is newly appearing or actively increasing in size should be investigated, even if it is not painful. Rapid growth is considered a strong indicator for further evaluation.
Specific physical characteristics signal a heightened risk for malignancy, necessitating specialist review. These include any lump that measures five centimeters or larger, approximately the size of a golf ball. A lump that feels fixed or tethered to the underlying deep tissues, rather than being easily movable, is also a concerning sign. Any mass associated with persistent pain or nerve symptoms like numbness or tingling should be promptly evaluated.