What Is a Teratoma?

Medically Reviewed by Dan Brennan, MD on May 15, 2021

Teratomas are rare tumors that may hold different types of tissue such as bone, teeth, muscle, and hair. They’re mostly found in the ovaries, testicles, and tailbone, but also sometimes grow in the nervous system and abdomen.

A teratoma may be cancerous or benign, depending on its structure. Scientists have long regarded them as puzzling. Some believe they may be the clue to understanding cancer.

Not all types of teratoma are cancerous. Immature teratomas are more likely to become cancerous. Mature teratomas tend to be benign, or non-cancerous.

Mature teratomas can present in different ways. They may be:

  • Solid – made of tissue, but not enclosed.
  • Cystic – contained by a sac.
  • Mixed – having both cystic and solid parts.

Mature teratomas are often found in ovaries, particularly in the ovaries of premenopausal women. The longer it remains inside your body, the more likely it may become cancerous.

There’s a rare type of teratoma known as fetus in fetu, or fetus within a fetus. This type of teratoma looks like a small fetus without an amniotic sac or placenta, and it occurs in about 1 in 500,000 people. It’s been theorized that fetus in fetu teratomas are the remains of a twin that was unable to develop and was enveloped by the surviving sibling. Over 90% of fetus in fetu are found before a child is 18 months of age.

Teratomas happen when complications arise during your cells’ differentiation process. In particular, they develop in your body’s germ cells, which are undifferentiated. This means they can turn into any type of cell – from egg and sperm to hair cells.

As a baby develops, their germ cells start moving to various places in the body to become differentiated cells, such as eggs in the ovaries and sperm in the testicles. This is why teratomas are usually found in ovaries or testicles and contain the following:

  • Hair
  • Teeth
  • Wax
  • Oil
  • Skin 

In general, you will experience the following if you have a teratoma:

  • Swelling
  • Bleeding
  • Pain

You will have more symptoms depending on what kind of teratoma you have. Some teratomas can be visible, such as tailbone teratomas. Others are not visible, so make sure to see a doctor if you are experiencing the above symptoms. Getting an early diagnosis of your condition is beneficial to successful treatment.

Symptoms of sacrococcygeal (tailbone) teratoma. Although this is the most common type of tumor in children and newborns, it generally doesn't occur often. These teratomas can be visible, but may not always be, since they can grow inside and outside the body near the tailbone area.

Besides a visible tumor in the tailbone area, other symptoms include:

  • Leg weakness, since the tumor is in the lower back
  • Pain during urination
  • Swelling in the pubic area
  • Difficulty holding in urine
  • Abdominal pain
  • Constipation 

Symptoms of testicular teratoma. You may have testicular teratoma if you see a lump or lumps in your testicles. You may also experience swelling in the area. Although it can occur at any age, testicular teratoma usually occurs when you’re in your twenties.

Symptoms of ovarian teratoma. The main symptom of ovarian teratoma is intense pain in your abdomen. As ovarian teratomas grow larger, they can put a lot of pressure on your ovary, causing it to twist. This can jeopardize your ovary’s blood supply.

These usually occur during the childbearing years. On average they occur at the age of 30 years. Ovarian teratomas have a wide range of sizes, from less than half an inch to over 17 inches in diameter.

Around 98% of ovarian teratomas are benign, but the remaining 2% can eventually become cancerous.

It is not always easy to tell when you have a teratoma. Often teratomas look like cysts, or they may not be visible at all.

If you see a lump on your body, you should book an appointment with your doctor. If your doctor suspects you have a teratoma, they will ask questions about your general health and medical history and do a physical exam. 

Your doctor may also request tests such as:

  • X-ray, ultrasound, bone scans, MRI, and CT to see where the tumor is and contain its spread.
  • Blood tests to check hormone levels that may indicate the presence of a tumor. 
  • Biopsy to see if the teratoma is cancerous.

If your teratoma has spread, is cancerous, or is likely to become cancerous, your doctor may suggest removing it through surgery. They may also suggest treating it with chemotherapy and radiation. Your treatment will depend on your age, health, and medical history. 

Show Sources


American Cancer Society Journals: “The evolution of mature teratoma from malignant testicular tumors.

‌‌Current Topics in Pathology: “Experimental Teratoma.”

‌‌Indian Journal of Surgery: “Fetus-In-Fetu or Well-Differentiated Teratoma- A Continued Controversy.”

‌‌Journal of Pediatric Surgery: “Congenital metastatic cervical teratoma: Diagnostic and management considerations.”

‌‌Journal of Pediatric Surgery Case Reports: “Giant sacrococcygeal teratoma in newborn: A rare case.”

‌‌Journal of Surgical Case Reports: “Fetus-in-fetu: a pediatric rarity.”

‌‌National Cancer Institute: “teratoma.”

‌‌Obstetrics and Gynecology: “Immature teratoma of the ovary,” “Mature cystic teratoma: a clinicopathologic evaluation of 517 cases and review of the literature.”

‌‌Przeglad Menopauzalny = Menopause Review: “Malignant transformation in mature cystic teratoma of the ovary: a retrospective study of eight cases and review of literature.”

Wheeler, J. The Human Teratomas, Humana Press, 1983.

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