A teratoma is a rare type of germ cell tumor that may contain immature or fully formed tissue, including teeth, hair, bone and muscle. Teratomas may be cancerous or noncancerous, and they can affect people of all ages. Treatment involves surgical removal. Cancerous teratomas may require chemotherapy, radiation therapy or other cancer treatments.


What is a teratoma?

A teratoma is a type of germ cell tumor (a tumor that starts in your reproductive cells). Teratomas can contain many different types of tissue, including bone, muscle, teeth and hair. They may be benign (noncancerous) or malignant (cancerous).


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Where can teratomas be found?

Teratomas most commonly form in the ovaries, testes or tailbone (coccyx) — but they can occur anywhere in the body.

Who do teratomas affect?


Teratomas can affect people of all ages. Some teratomas form during development in the uterus.

How common are teratomas?

Teratomas are considered rare overall. The frequency at which they occur varies depending on where the tumor is found:

  • Sacrococcygeal teratomas form in your tailbone. They’re the most common tumor in newborn babies, occurring in 1 out of every 20,000 to 40,000 births. They also occur more frequently in people assigned female at birth (AFAB) than in people assigned male at birth (AMAB).
  • Ovarian teratomas form in your ovaries. They are the most common ovarian germ cell tumor affecting people AFAB under the age of 45. Ovarian teratomas account for 10% to 20% of all ovarian tumors.
  • Testicular teratomas form in your testes. They are the second most common germ cell tumor affecting people AMAB between the ages of 20 and 35. They account for 4% to 9% of all testicular tumors.

Fetus in fetu teratomas

There is another, very rare type of teratoma called fetus in fetu (fetus within a fetus). This type of teratoma is made up of living tissue and it often takes on the appearance of a malformed fetus. However, because there is no placenta or amniotic sac, the fetus has no chance of development. Fetus in fetu teratomas only occur in twins who both share the same placenta and have their own sac of amniotic fluid.

There are two primary theories regarding fetus in fetu teratomas:

  • The teratoma is the remains of a twin that couldn’t develop in the womb and was enveloped by the body of the surviving twin.
  • The teratoma is a more developed dermoid cyst (a noncancerous lump present at birth).
  • Fetus in fetu teratomas occur in 1 out of every 500,000 people. In about 90% of these cases, the teratoma is discovered within the first 18 months of life.

Are there different types of teratomas?

Teratomas are divided into two main categories: mature and immature.

  • Mature: This type of teratoma is usually noncancerous. However, mature teratomas are more likely to grow back once surgically removed.
  • Immature: This type of teratoma is more likely to grow into cancer. Immature teratomas may contain elements of somatic (not germ cell) cancers, such as sarcoma, carcinoma or leukemia.

Symptoms and Causes

What are the symptoms of a teratoma?

People with teratomas may not show any symptoms at first. Once symptoms develop, they can vary significantly depending on where the tumor is located. General teratoma symptoms may include:

  • Pain.
  • Bleeding.
  • Swelling.
  • Slightly elevated levels of the hormone BhCG (beta-human chorionic gonadotropin).
  • Slightly elevated levels of tumor marker AFP (alpha-fetoprotein).

Certain types of teratomas often exhibit specific symptoms:

Sacrococcygeal (tailbone) teratoma

Sacrococcygeal teratomas can form inside or outside your body in the tailbone area. Possible symptoms include:

Ovarian teratoma

A main symptom of ovarian teratoma is intense abdominal or pelvic pain. This occurs when the growing mass places excess pressure on the ovary.

In some instances, ovarian teratomas may be accompanied by NMDA encephalitis — a rare condition that can lead to severe headaches, confusion and psychosis.

Testicular teratoma

The primary symptom of testicular teratoma is a lump or swelling in the testicle. In some cases, people with testicular teratoma may not show any symptoms.

What is the cause of a teratoma?

Teratomas form in germ cells, which are undifferentiated — meaning they can turn into any type of cell. A teratoma develops when there are disruptions during your cells’ differentiation process.

Diagnosis and Tests

How is a teratoma diagnosed?

If your healthcare provider suspects that you have a teratoma, they will perform a physical examination and ask you questions about your symptoms and medical history. They may also order tests, including:

With the development of imaging technology, healthcare providers can sometimes diagnose a teratoma in the fetal stage of development.

Management and Treatment

How is a teratoma treated?

First, your healthcare provider will determine if the teratoma is cancerous or noncancerous. Nearly all teratomas should be removed when discovered. Even if they aren’t cancerous, they can still grow rapidly or rupture, leading to other problems. If your teratoma is cancerous, your healthcare provider may recommend chemotherapy, radiation therapy or a combination of the two in addition to surgical removal.

Teratomas detected in the fetal stage

If a teratoma is detected during the fetal stage, your healthcare provider will monitor your pregnancy closely. Small teratomas usually aren’t threatening, and a normal vaginal delivery can be planned. Large teratomas may require early delivery via C-section. Rarely, fetal surgery is necessary to remove the teratoma before it leads to serious complications.

Before planning your treatment, your healthcare provider will take your unique situation into account. Treatment will depend on several factors, including your age, medical history, overall health and personal preferences.

Outlook / Prognosis

Can you survive a teratoma?

Yes. Most teratomas — even cancerous ones — have excellent survival rates with early diagnosis and treatment.

Living With

When should I see my healthcare provider?

Anytime you notice a new lump or bump on your skin, you should schedule a visit with your healthcare provider. They can run the appropriate tests and determine a diagnosis. If you’ve already been diagnosed with a teratoma, call your provider any time you develop pain or other new symptoms.

A note from Cleveland Clinic

Teratomas are rare — and in most cases, they’re noncancerous. However, even cancerous teratomas can be treated successfully with prompt diagnosis and treatment. If you’ve been diagnosed with a teratoma, ask your healthcare provider for resources so you can make an informed decision about your health.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 11/16/2021.

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