Introduction

A tumor is any type of abnormal growth, whether cancerous (malignant) or noncancerous (benign). Tumors that originate in the heart are called primary tumors. They may develop in any of the heart tissues and may be cancerous or noncancerous. Primary heart tumors are rare, occurring in fewer than 1 of 2,000 people. In adults, the most common type of noncancerous primary heart tumor is a myxoma, which accounts for about 50% of such tumors. In infants and children, the most common type of noncancerous primary heart tumor is a rhabdomyoma, which accounts for about 40% of such tumors. Fibromas are the second most common noncancerous primary tumors in infants and children. Other tumors are extremely rare.

Myxomas usually develop in the heart's left upper chamber (atrium). They may develop from embryonic cells located in the inner layer (lining) of the heart's wall. Rhabdomyomas, which typically occur in groups, usually grow within the heart wall and develop directly from the heart's muscle cells. Rhabdomyomas commonly develop during infancy or childhood, often as part of a rare disease called tuberous sclerosis. Fibromas, which typically occur as a single tumor, usually grow on heart valves and develop from the heart's fibrous tissue cells.

Tumors that originate in some other part of the body--usually the lung, breast, blood, or skin--and then spread (metastasize) to the heart are called secondary tumors. They are always cancerous. Secondary heart tumors of the heart are 30 to 40 times more common than primary heart tumors but are still uncommon. About 10% of people who have lung or breast cancer--two of the most common cancers--and about 75% of people with malignant melanoma (which is becoming increasingly common) have metastases to the heart.

Symptoms

Heart tumors may cause no symptoms, minor symptoms, or symptoms of life-threatening heart malfunction, which resemble those of other heart diseases but which develop suddenly. For example, tumors may cause heart failure, abnormal heart rhythms (arrhythmias), or a decrease in blood pressure caused by bleeding into the pericardium, the sac that envelops the heart. Heart murmurs develop in about half of the people who have tumors that develop near or on a heart valve (such as myxomas and fibromas), because blood does not flow through the valve normally. Noncancerous tumors can be as deadly as cancerous ones if they interfere with the function of the heart.

Heart tumors, especially myxomas, may degenerate so that pieces of them break off and travel through the bloodstream (becoming emboli). Emboli may lodge in small arteries and block blood flow. Also, blood clots that form on the surface of tumors, such as myxomas, may break off as emboli and block arteries. Symptoms due to emboli depend on which tissues or organ is supplied by the blocked artery.

Diagnosis

Primary heart tumors are difficult to diagnose because they are relatively uncommon and because their symptoms resemble those of many other disorders. Doctors may suspect a primary heart tumor in people who have heart murmurs, abnormal heart rhythms, unexplained symptoms of heart failure, or unexplained fever (which may be due to a myxoma). Secondary heart tumors are suspected when people who have cancer elsewhere in the body come to a doctor with symptoms of heart malfunction.

If a tumor is suspected, echocardiography (see Section 3, Chapter 21) is usually performed to confirm the diagnosis. For this procedure, a probe that emits ultrasound waves is passed over the chest, producing an image of heart structures. If another view of the heart is needed, the probe can be passed down the throat into the esophagus to record signals from just behind the heart. This procedure is called transesophageal echocardiography. Computed tomography (CT) (see Section 3, Chapter 21) or magnetic resonance imaging (MRI) can provide additional information (see Section 3, Chapter 21) Coronary angiography (see Section 3, Chapter 21). can produce an outline of a heart tumor that can be seen on x-rays, but this procedure is rarely needed.

If a tumor is detected in the right side of the heart, a small sample may be removed for examination under a microscope (biopsy). The sample is removed with a catheter that is inserted into a vein, usually in the leg, and threaded toward the heart in a procedure called cardiac catheterization (see Section 3, Chapter 21). This procedure helps doctors identify the type of tumor and select the appropriate treatment. Biopsy of tumors on the left side is rarely performed, because the risks of the procedure outweigh the benefits.

Treatment

A single small noncancerous primary heart tumor can be surgically removed, usually resulting in a cure. If a large noncancerous primary tumor is significantly reducing blood flow through the heart, removal of the part of the tumor that does not grow into the heart wall may improve heart function. However, if a large part of the heart wall is involved, surgery may be impossible.

In about half of newborns who have noncancerous rhabdomyomas, tumors regress without treatment; in the other half, the tumors do not grow any larger and do not require treatment. In infants and children, a fibroma may be successfully removed if it does not affect the wall between the ventricles (septum). Tumors that affect this wall usually also affect the electrical conduction system of the heart and cannot be surgically removed. Children with this type of tumor usually die of an abnormal heart rhythm at an early age. If a fibroma is large, blocks blood flow, and has grown into the surrounding tissue, heart transplantation may be required.

Primary cancerous tumors cannot be surgically removed and are usually fatal.