Finding a lump under the skin can be worrying. In many cases, these lumps are harmless and may be caused by conditions such as lipomas, cysts, or inflammation. However, in rare cases, a growing lump under the skin may be linked to a more serious condition such as sarcoma.

Sarcoma is a rare type of cancer that develops in connective tissues such as muscles, fat, nerves, blood vessels, and bones. Knowing the warning signs and understanding when a lump should be evaluated by a doctor can help with early detection.

If you want to learn more about the disease itself, see our guide: What is sarcoma?

What causes a lump under the skin?

A lump under the skin can appear for many different reasons. Most of the time, these lumps are benign and not dangerous.

Lipoma

A lipoma is one of the most common causes of a soft lump under the skin. It is a benign tumor made of fat tissue and usually feels soft, movable, and painless.

Cysts

Cysts are fluid-filled sacs that can form under the skin. They may appear as a small lump under the skin and are usually harmless.

Inflammation or infection

Sometimes a swelling on the arm or leg may develop due to infection, inflammation, or injury. In these cases the lump may be tender or temporarily swollen.

When can a lump under the skin be dangerous?

Although most lumps are harmless, certain warning signs should not be ignored.

A lump that keeps growing

A lump that grows over time should always be evaluated by a healthcare professional. Rapid growth can sometimes indicate a tumor developing in deeper tissues.

Size larger than 5 centimeters

A large lump under the skin, especially one larger than 5 cm, should be examined by a doctor.

Lump located deep in the muscle

A lump in the thigh or muscle that feels deep and does not move easily under the skin may require further medical tests.

Persistent bone or muscle pain

In some cases, persistent bone pain or discomfort around a lump may require medical evaluation.

Could a lump in the muscle be sarcoma?

In rare cases, a lump in the muscle or soft tissue may be a sign of sarcoma. Soft tissue sarcomas can develop in muscles, fat tissue, blood vessels, or nerves. However, it is important to remember that most lumps are not cancer. Only medical imaging and diagnostic tests can determine the exact cause.

Learn more about different tumor types here: Types of sarcoma

When should you see a doctor?

You should consider seeing a doctor if you notice:

• a lump under the skin that continues to grow
• a swelling on the leg or arm that does not go away
• a lump in the thigh or muscle that becomes painful
• a rapidly growing lump
• persistent bone pain

Doctors may recommend imaging tests such as ultrasound, MRI, or CT scans to determine the cause of the lump.

Why early diagnosis matters

Early diagnosis is especially important when dealing with rare cancers such as sarcoma. Detecting tumors early can improve treatment options and outcomes.

If you notice a growing lump under the skin, swelling in the muscle, or unusual bone pain, it is best to consult a qualified healthcare professional.

FAQ

Is a lump under the skin always cancer?

No. Most lumps under the skin are benign and may be caused by lipomas, cysts, or inflammation. However, any lump that grows or causes symptoms should be evaluated by a doctor.

Can a lump in the muscle be sarcoma?

In rare cases, a lump in the muscle may be a soft tissue sarcoma. Medical imaging and diagnostic tests are necessary to determine the exact cause.

When should I worry about a lump under the skin?

You should seek medical advice if the lump grows quickly, becomes painful, is larger than 5 centimeters, or does not move easily under the skin.

What tests are used to diagnose a lump?

Doctors may use ultrasound, MRI scans, CT scans, or a biopsy to determine the nature of a lump.