Your pathology report for immature teratoma of the ovary

by Emily Goebel, MD FRCPC
August 25, 2025

An immature teratoma is a rare type of ovarian tumour that contains both mature tissues, such as skin or fat, and immature tissues, typically composed of developing nerve cells. The word immature is used because some of the tissues inside the tumour look similar to embryonic or early developmental tissue under the microscope. Unlike mature teratomas, which are benign (noncancerous), immature teratomas are considered malignant, meaning they can behave like cancer.

Who gets immature teratoma?

Immature teratomas are most often diagnosed in children, teenagers, and young women. Most cases occur before the age of 30. They are the second most common type of malignant germ cell tumour of the ovary.

What are the symptoms of immature teratoma?

Most people with an immature teratoma develop symptoms related to the presence of a pelvic mass. Common symptoms include:

• Abdominal or pelvic pain.

• A feeling of fullness or swelling in the abdomen.

• A noticeable lump in the pelvic area.

• Irregular menstrual cycles in some cases.

Occasionally, blood tests may show high levels of a protein called alpha-fetoprotein (AFP). While AFP can sometimes be elevated in immature teratomas, it usually suggests that another type of germ cell tumour called a yolk sac tumour is also present.

What causes immature teratoma?

The exact cause of immature teratoma is not known. Like mature teratomas, these tumours arise from germ cells, which are special cells in the ovary that normally develop into eggs. Scientists believe that genetic or developmental changes in these germ cells cause them to grow into both mature and immature tissues.

How is this diagnosis made?

The diagnosis is usually made after surgery to remove the tumour. Imaging studies, such as ultrasound or MRI, can detect the mass but cannot determine whether the tumour is immature or mature. A pathologist makes the final diagnosis by examining the tumour under the microscope. Special tests, such as immunohistochemistry, may be used in difficult cases to confirm the diagnosis.

What does immature teratoma look like under the microscope?

When examined under the microscope, immature teratomas contain a mix of tissues from different germ layers, such as skin, cartilage, or intestinal lining. The key feature, however, is the presence of immature tissue, especially immature nerve tissue. Pathologists often see immature neuroectodermal structures, which look like small round collections of developing nerve cells.

Because other types of ovarian germ cell tumours can look similar, pathologists carefully search the tumour for areas of yolk sac tumour or other elements. This is especially important if AFP levels are elevated.

How do pathologists grade immature teratoma?

For immature teratomas, pathologists use the word grade to describe the amount of immature brain tissue seen in the tumour. Brain tissue is important because it is the most common type of immature tissue in these tumours. The grade can only be determined after the tumour has been removed and examined carefully under the microscope.

Pathologists divide immature teratomas into three grades based on how much immature brain tissue is present:

• Grade 1: Only a very small amount of immature brain tissue is seen. To qualify as grade 1, the area of immature tissue must be smaller than one low-power field of view when the tumour is examined under the microscope.

• Grade 2: A moderate amount of immature brain tissue is found. In this case, the immature tissue occupies an area larger than one low-power field but no more than three low-power fields of view.

• Grade 3: Large areas of immature brain tissue are present. For grade 3, the immature tissue covers more than three low-power fields of view when examined under the microscope.

Using this information, pathologists often group immature teratomas into low grade and high grade categories. Grade 1 tumours are considered low grade and generally have a very good prognosis, especially when they are confined to the ovary. Grade 2 and grade 3 tumours are considered high grade because they are more likely to spread to other parts of the body and may require additional treatment such as chemotherapy.

What is gliomatosis peritonei?

Some patients with immature teratoma develop a condition called gliomatosis peritonei, which means deposits of mature glial tissue (a type of nerve support tissue) are found in the lining of the abdomen. Although gliomatosis peritonei is considered stage III disease, it usually behaves in a benign way and does not require aggressive treatment.

How is immature teratoma staged?

Immature teratoma is staged using the TNM system and the FIGO system for ovarian cancer. Staging describes how far the tumour has spread at the time of diagnosis.

• Stage I: The tumour is confined to one or both ovaries.

• Stage II: The tumour has spread to other organs in the pelvis, such as the uterus or fallopian tubes.

• Stage III: The tumour has spread to the lining of the abdomen or to lymph nodes.

• Stage IV: The tumour has spread to distant organs such as the liver or lungs.

Staging helps doctors determine the best treatment and predict the likely outcome.

What is the prognosis for immature teratoma?

The prognosis for immature teratoma depends mainly on the tumour’s stage and grade.

• Stage I tumours that are completely removed have an excellent prognosis, with survival rates close to 100%.

• For higher-stage or higher-grade tumours, treatment may include chemotherapy in addition to surgery.

• Even in advanced cases, overall survival rates are very good, greater than 90% in most studies.

Patients with gliomatosis peritonei typically have an excellent outcome, and treatment is not usually needed for this finding.

What is the difference between immature and mature teratoma?

The key difference is that a mature teratoma contains only fully developed tissues such as skin, fat, or bone and is benign. An immature teratoma contains embryonic or immature tissues, usually from the nervous system, and is malignant. Immature teratomas have the potential to grow more quickly, spread to other parts of the body, and recur after treatment, which is why grading and staging are so important.

Questions to ask your doctor

• What grade and stage is my immature teratoma?

• Were there any signs of spread outside the ovary?

• Do I need chemotherapy or is surgery alone enough?

• Was gliomatosis peritonei seen in my case, and what does it mean?

• What is my long-term outlook?

• How often will I need follow-up testing after treatment?