What is a hamartoma?

A hamartoma is a noncancerous growth composed of an abnormal mixture of normal tissues, typically found in the part of the body where the growth occurs. The word “hamartoma” comes from a Greek term meaning “to go wrong,” referring to how the tissue develops in a disorganized way.

Unlike a typical tumor, which starts from a single cell that begins to grow uncontrollably, a hamartoma is formed from mature but disorganized cells that belong to that specific organ. It can be thought of as a small patch of tissue that developed incorrectly, but is not harmful or cancerous.

Where are hamartomas found?

Hamartomas can develop anywhere in the body, but they are most often found in the following locations:

• Lungs: A hamartoma in the lungs may contain cartilage, fat, and connective tissue.

• Liver: A hamartoma in the liver often appears as a small, well-defined nodule made of liver cells and bile ducts.

• Kidneys: A type of hamartoma called an angiomyolipoma is made up of blood vessels, smooth muscle, and fat.

• Skin: A skin hamartoma may look like a birthmark or small lump and can include extra oil glands, hair follicles, or blood vessels.

• Brain: A hamartoma in the brain may contain a mixture of nerve cells, glial (support) cells, and blood vessels.

Most hamartomas are discovered by chance during imaging, surgery, or testing performed for other medical reasons.

What is the difference between a hamartoma and a tumor?

The word tumor means “a mass or swelling” and can describe both benign (noncancerous) and malignant (cancerous) growths. A hamartoma is a special type of benign tumor that differs from most other tumors in several important ways:

• The tissues inside a hamartoma are normal for that organ, but they are arranged in an abnormal or disorganized pattern.

• The cells are mature and well-differentiated, which means they look and behave like normal cells rather than cancer cells.

• Hamartomas do not invade nearby tissues or metastasize (spread) to other parts of the body.

By contrast, malignant tumors are made up of cells that grow uncontrollably, invade surrounding tissues, and can spread through the blood or lymphatic system.

Are hamartomas dangerous?

Hamartomas are benign and usually harmless. However, depending on their size and location, they can sometimes cause problems by pressing on nearby organs or interfering with normal function.

• A lung hamartoma might show up as a small spot on an X-ray, but it usually causes no symptoms.

• A brain hamartoma that grows near important nerves or brain structures can sometimes cause seizures or other neurological symptoms.

Most hamartomas grow very slowly and do not require treatment unless they cause symptoms or complications.

What causes a hamartoma?

The exact cause of hamartomas is not fully understood. Most are thought to develop because of minor developmental errors that occur when tissues form before birth. These errors cause the cells to grow in the wrong pattern, but not in an uncontrolled or cancerous way.

Some hamartomas are linked to genetic conditions that cause multiple hamartomas to form in different parts of the body. Examples include:

• Cowden syndrome: This condition is caused by mutations in a gene called PTEN and can lead to hamartomas in the skin, thyroid, breast, and digestive tract.

• Tuberous sclerosis complex: This condition is caused by mutations in the TSC1 or TSC2 genes and can lead to hamartomas in the brain, kidneys, lungs, and heart.

Most hamartomas, however, are sporadic, which means they occur by chance and are not inherited.

What types of tissue are found in a hamartoma?

The types of tissue found in a hamartoma depend on where it forms. In every case, the tissues are normal for that organ, but they are arranged in a disorganized pattern.

• A lung hamartoma may contain cartilage, fat, connective tissue, and occasionally bone.

• A kidney hamartoma (angiomyolipoma) contains blood vessels, smooth muscle, and fat.

• A skin hamartoma may include an overgrowth of hair follicles, oil glands, or blood vessels.

• A brain hamartoma can contain a mix of neurons (nerve cells), glial (support) cells, and small blood vessels.

Each hamartoma is unique, reflecting the specific tissues that normally belong to that part of the body.

How is a hamartoma diagnosed?

A hamartoma is often discovered incidentally on an imaging test such as an X-ray, CT scan, or MRI. To confirm the diagnosis, a doctor may remove a small sample of tissue for examination under a microscope.

A pathologist makes the diagnosis by identifying the mixture of mature, disorganized tissues that are native to the organ but not arranged normally. These findings distinguish a hamartoma from both normal tissue and other types of tumors.

What is the prognosis for a person with a hamartoma?

The prognosis is excellent. Hamartomas are benign and do not spread to other parts of the body. In most cases, no treatment is required. If the growth causes symptoms or pressure on nearby organs, it can be removed surgically. Once removed, recurrence is infrequent.

Questions to ask your doctor

• What type of hamartoma do I have, and where is it located?

• Will I need treatment, or can it be safely monitored?

• Could my hamartoma be related to a genetic condition?

• Should I or my family members consider genetic testing?

• Is there any chance this could turn into cancer?