Ovary -

Mature cystic teratoma

This article was reviewed and updated on September 2, 2019.

by Jason Wasserman, MD PhD FRCPC

Quick facts:

  • A mature cystic teratoma is a non-cancerous ovarian tumour. 

  • It is the most common type of non-cancerous tumour ovarian tumour in adults.

  • Unlike most tumours which are made up of a single type of tissue, teratomas can include multiple types of tissue  such as skin and thyroid tissue.

  • A tumour made up mostly of skin is called a dermoid cyst.

The ovaries

The ovaries are small, round, paired organs that are attached to the uterus by the fallopian tubes. The ovaries contain large cells called eggs. In adult women, these eggs are released from the ovary during ovulation. The eggs are a special type of cell called a germ cell. They are called germ cells because they have the potential to turn into any other type of cell in the body (the word germ comes from the Latin word for ‘seed’).

What is a mature teratoma?

A mature teratoma is a non-cancerous (benign) tumour that develops from the germ cells in the ovary. It is the most common non-cancerous ovarian tumour in adults.


Because teratomas start from a type of cell that has the ability to turn into any other type of cell, teratomas may contain a variety of tissue types including skin, teeth, hair, brain, and muscle. In fact, any type of tissue can be found in a teratoma.


Despite this potential, most teratomas are made up almost entirely of one or two types of tissue with skin being the most common. Many tumours made of skin contain a hollow center called a cyst

Some mature teratomas are given special names:

  • Dermoid cyst - This is a teratoma made up almost entirely of skin.

  • Struma ovarii - This is a teratoma that contains thyroid gland tissue.

Most teratomas are called ‘mature’ because, when viewed under a microscope, the tissue inside the tumour looks like the normal mature tissue found in adults. For example, the ‘skin’ inside a mature teratoma would look the same under the microscope to the skin on your arm.

The diagnosis of mature teratoma is usually only made after the entire tumour has been removed and the tissue sent to a pathologist for examination.​

Tumour size

This is the size of the tumour measured in centimeters (cm). Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.

Immature tissue

As described above, mature teratomas contain tissue that resembles adult tissue. Some teratomas, however, also contain tissue immature tissue which is normally found in a developing human (embryo or fetus). Your pathologist will closely examine the tumour to make sure there is no immature tissue before making the diagnosis of mature teratoma.

Why is this important? A mature teratoma should contain no immature tissue.

Cancer in a teratoma
Mature teratomas are non-cancerous (benign) tumours. However, in rare situations, a cancer (a malignant tumour) can develop from one of the tissues inside the teratoma.

Because teratomas are made up of different types of tissue, almost any type of cancer can start inside of a teratoma. For example, if a cancer starts in an area of tissue that looks like skin, the cancer will look very similar to adult type skin cancer.


In situations where a cancer is seen inside of a teratoma, the diagnosis will include both the mature teratoma and the name of the cancer.

Why is this important? A cancer found inside a mature teratoma can spread to other parts of your body. Talk to your doctor about the treatment options for this type of cancer.

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