Myxoma: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 28, 2026

A myxoma is a noncancerous tumor made of scattered cells in a soft, gel-like background called myxoid tissue. The gel-like material is what gives this tumor its name and its soft, jelly-like feel.

Myxomas do not spread to other parts of the body and do not turn into cancer. They grow slowly, and most are cured by removal.

Myxomas can develop in many places, including the heart, the muscles of the arms and legs, the skin, near a joint, and inside the ovary. The location determines the symptoms and the treatment, so your report will state where the tumor was found.

This article gives an overview of myxomas and explains what the findings in your pathology report mean.

What are the types of myxoma?

Cardiac myxoma. The most common tumor to start in the heart, usually in the upper left chamber. It matters more than its size suggests, because pieces can break off and travel in the bloodstream. Our article on cardiac myxoma covers this type in detail.
Intramuscular myxoma. Develops inside a large muscle, most often in the thigh, shoulder, or buttock. It usually appears as a painless lump deep in the muscle.
Juxta-articular myxoma. Develops next to a joint, most often the knee, and can cause tenderness or swelling near the joint.
Cutaneous myxoma. A small, soft nodule in the skin. Several of these appearing together can be a sign of an inherited condition.
Ovarian myxoma. A rare tumor of the ovary, usually found on imaging done for another reason.

A tumor in the jaw may also be called a myxoma, or an odontogenic myxoma. That tumor arises from tooth-forming tissue and is a different condition from the ones described here.

What are the symptoms of a myxoma?

Symptoms depend on where the tumor is and how large it has grown:

Heart. Shortness of breath, chest pain, a sensation of strong or irregular heartbeats, or fainting. Symptoms may change with body position.
Muscle. A slow-growing, painless lump deep in the muscle, sometimes noticed only when it becomes large.
Near a joint. Tenderness, swelling, or discomfort with movement.
Skin. One or more small, soft bumps, usually painless.
Ovary. Often no symptoms. A large tumor may cause pelvic pressure or pain.

What causes a myxoma?

For most people, the cause is unknown. Most myxomas occur on their own, with no family history and no identifiable trigger.

Many intramuscular myxomas have a change in a gene called GNAS, which develops in the tumor cells during a person’s lifetime and is not inherited. The same change is found in a bone condition called fibrous dysplasia. When a person has both intramuscular myxomas and fibrous dysplasia, the combination is known as Mazabraud syndrome.

Two inherited conditions are linked to myxomas:

Carney complex. This condition causes myxomas in the heart and skin, along with unusual skin pigmentation and hormone-producing tumors. It is caused by a change in a gene called PRKAR1A, and each child of an affected parent has a 50% chance of inheriting it.
Mazabraud syndrome. This condition combines intramuscular myxomas with fibrous dysplasia, a condition in which fibrous tissue replaces normal bone.

Your doctor may consider one of these conditions if you have more than one myxoma or a heart myxoma at a young age. The same applies if you have a myxoma along with the other features described above.

How is the diagnosis made?

A pathologist makes the diagnosis after examining tumor tissue under a microscope. For a tumor in the heart, the tissue comes from surgery to remove it. For a tumor in a muscle or the skin, the tissue may come from a biopsy or from removal of the whole tumor.

Under the microscope, a myxoma is made of long, thin spindle cells spread thinly through abundant myxoid tissue, which looks light blue on a routine slide. The cells may sit singly or in small groups.

Your report may describe the tumor as hypocellular (few cells) or hypercellular (many cells). Most myxomas have few cells. The report may also mention degenerative changes, which develop in a tumor that has been present for a long time. These include bleeding, scarring (fibrosis), small fluid-filled spaces (cysts), and clumps of calcium c(calcification). None of these changes make the tumor cancerous.

How is a myxoma different from a cancer?

Several cancers also contain myxoid tissue, including myxofibrosarcoma and myxoid liposarcoma. Separating them from a myxoma is one of the pathologist’s main jobs when examining this tissue.

A myxoma contains few cells, and those cells look uniform, with no dividing cells and few blood vessels. Myxoid cancers contain more cells, abnormal-looking cells, and a network of small, branching blood vessels running through the tissue.

This distinction can be difficult on a small biopsy, so your report may recommend removal of the whole tumor before a final diagnosis is given.

Margins

A margin is the edge of tissue cut by the surgeon. Your report may note whether tumor reaches the cut edge.

For a myxoma, a positive margin does not carry the meaning it does for cancer. It does raise the chance that the tumor comes back in the same place. This matters most for tumors in muscle, which blend into surrounding tissue and can be difficult to remove completely.

What is the prognosis?

The outlook is excellent. A myxoma is noncancerous, does not spread, and does not become cancer.

Most myxomas are cured by removal and do not come back. Tumors that come back usually do so when some tissue is left behind. People with Carney complex may develop new myxomas over time, including in the heart, and are followed with regular checks for that reason.

What happens after the diagnosis?

Surgery. Removing the tumor is the usual treatment. For a myxoma in the heart, removal is recommended promptly because fragments may travel through the bloodstream.
Observation. A small myxoma in a muscle or the skin that causes no symptoms may be watched instead of removed.
Follow-up. Routine follow-up is usually not needed after removing a single myxoma. People with Carney complex are followed long term, including regular heart imaging.
Assessment for an inherited condition. Consider this for anyone with more than one myxoma, a heart myxoma at a young age, or a myxoma alongside bone or skin findings.

Questions to ask your doctor

Where was my myxoma, and was it all removed?
How was this separated from a cancer that contains similar tissue?
Is there a chance it will come back?
Do I need follow-up imaging, and for how long?
Should I be assessed for Carney complex or Mazabraud syndrome?
Do my family members need to be checked?
Which symptoms should prompt me to call?