Soft tissue sarcomas (STS) are a group of rare cancers that develop in supportive tissues, such as fat, muscle, and nerves. While most lumps are benign, this article describes the typical physical characteristics associated with STS. Only a medical professional can provide an accurate diagnosis.
Defining Soft Tissue Sarcoma
Soft tissue sarcoma is a diverse collection of cancers originating in the body’s connective tissues, which connect, support, and surround other structures and organs. The term “soft tissue” encompasses fat, muscle, blood vessels, tendons, ligaments, and tissues around joints, meaning sarcomas can form almost anywhere.
This group of cancers is distinct from bone sarcomas. Although soft tissues are found throughout the body, STS is most commonly found in the arms and legs. There are more than 50 different subtypes, classified based on the cell type of origin, such as liposarcoma from fat cells or leiomyosarcoma from smooth muscle.
Physical Characteristics of the Lump
The physical characteristics of a soft tissue sarcoma vary, but certain features are frequently noted during examination. The mass is typically described as feeling firm or rubbery upon palpation, presenting as a solid structure beneath the skin. Consistency is not a definitive indicator, however, as some sarcomas can be soft, and some benign masses can feel hard.
The mobility of the lump relates to its depth within the tissue layers. A deep-seated sarcoma, lying beneath the fascia, may feel fixed or immobile because it is attached to underlying structures. A superficial sarcoma, located just under the skin, might be slightly movable, though a fixed mass raises more suspicion.
Sarcomas often grow quite large before they are noticed. Masses larger than five centimeters are more likely to be malignant and warrant immediate evaluation. Rapid growth over a period of weeks or months is also a concerning feature.
The Role of Pain and Associated Symptoms
Soft tissue sarcomas are often painless, especially in their early stages. This lack of discomfort is a common reason for delayed detection. The absence of pain does not rule out the possibility of a sarcoma.
Pain frequently occurs as the tumor grows larger and exerts pressure on surrounding structures. If the mass presses on a nerve, a patient may experience localized pain, tingling, or numbness. When a sarcoma is near a joint, its size can limit the normal range of motion, causing stiffness or difficulty moving the limb.
The tumor’s growth can lead to other localized symptoms, such as swelling in the surrounding area. If the tumor affects the flow of blood or lymph fluid, it may cause noticeable enlargement of the limb due to fluid accumulation, known as edema. Sarcomas located in the abdomen may cause a feeling of fullness, abdominal pain, or changes in bowel or bladder function.
Next Steps for Medical Evaluation
Finding any unexplained or growing lump should prompt a visit to a healthcare provider for evaluation. Clinicians are particularly concerned about masses that are firm, deep-seated, or measure greater than five centimeters in diameter. The initial steps begin with a thorough physical examination, where the doctor assesses the lump’s size, consistency, and mobility.
The next phase involves imaging tests to get a detailed look at the mass and its relationship to nearby structures. MRI (magnetic resonance imaging) is often the standard test for evaluating potential soft tissue sarcoma in the arms or legs, providing clear pictures of the tumor’s size and depth. An ultrasound may also be used as a first-line test to determine if the mass is solid or fluid-filled.
If imaging suggests a sarcoma, the definitive step is a biopsy, where a small tissue sample is removed for laboratory testing. Medical imaging and a biopsy are the only ways to confirm the nature of a mass.