A teratoma is a tumor that grows from germ cells, the cells that normally form eggs or sperm. Germ cells can develop into almost any kind of tissue. For this reason, a teratoma can contain a surprising mix of tissues, such as skin, hair, fat, cartilage, bone, and even brain tissue.
Teratoma is one of the most common tumors in babies and children. Most teratomas in children are noncancerous, and surgery to remove the tumor is often the only treatment needed. Teratomas in children also behave differently from teratomas in adults, so information written for adults may not apply to your child.
This article explains where teratomas occur in children, what mature and immature teratoma mean, and why the pathologist looks closely for yolk sac tumor. It also explains the other findings in your child’s teratoma pathology report.
Teratoma can occur at any age in childhood, from before birth through the teenage years, and girls are affected more often than boys. Where a teratoma grows depends strongly on the child’s age.
In a large Italian study of children and teenagers with teratoma, about 43% of tumors were in the ovary, and 30% were in the sacrococcygeal area. About 11% were in the testicle, and the chest and the back of the abdomen each accounted for about 5%.
Teratomas in children start with germ cells that grow uncontrollably. Before birth, germ cells travel through the body of the developing baby to reach the ovaries or testicles. Some germ cells can settle along the way, usually near the body’s midline. This explains why childhood teratomas often form along the midline, such as at the base of the spine, in the chest, and in the neck.
Most childhood teratomas are not inherited and do not run in families. Rarely, a teratoma is linked to an underlying genetic condition. Currarino syndrome is one example. In this inherited condition, a mass in front of the lower spine occurs together with a malformation of the anus or rectum and a notch in the sacral bone. Another is Klinefelter syndrome, which is associated with germ cell tumors in the chest in boys. When a hereditary condition like this is suspected, the family may be offered genetic testing.
Teratoma symptoms depend on where the tumor is growing in the body. Many teratomas cause no symptoms and are found on a routine ultrasound or exam.
The diagnosis of teratoma is made when a pathologist examines the tumor under a microscope. Before surgery, an ultrasound, CT scan, or MRI shows the size and location of the tumor. Teratomas often contain fat, fluid, and calcium, which imaging can suggest.
Doctors usually order blood tests before surgery, and the most important is alpha-fetoprotein (AFP), a protein made by yolk sac tumor, a type of cancerous germ cell tumor. A test for human chorionic gonadotropin (hCG) may also be done. A raised result suggests a cancerous germ cell tumor may be present along with the teratoma.
In most children, the surgeon removes the whole tumor in one operation. For a testicular or ovarian teratoma with normal blood tests, the surgeon may remove only the tumor and save the rest of the organ. For a very large tumor in the chest, a small biopsy is sometimes taken first.
Under the microscope, the pathologist identifies the different tissues in the tumor. The pathologist then looks carefully for immature tissue and for any cancerous germ cell tumor. Because these areas can be very small, pathologists examine many samples of the tumor, usually at least one for each centimeter of tumor size. Special stains, described below, help find small areas of yolk sac tumor.
Immunohistochemistry uses stains to show which proteins are present in cells. In a teratoma, it mainly looks for small areas of yolk sac tumor that are hard to see on routine slides. Your child’s report may list some of the following results.
Not every teratoma needs every stain, and the pathologist chooses stains based on what the tissue shows and on your child’s blood test results.
Pathologists divide teratomas into the types below, following the current WHO classifications and the College of American Pathologists (CAP) protocol for extragonadal germ cell tumors (version 5.0.0.1, 2025). The teratoma type is one of the most important findings in your child’s report.
For teratomas of the testicle, the WHO Classification of Urinary and Male Genital Tumors (5th edition, 2022) uses two further names. A prepubertal-type teratoma is usually found in young boys and is noncancerous. A postpubertal-type teratoma develops after puberty from abnormal germ cells in the testicle, and it can spread. The report may use either name, and the difference is explained in more detail below.
Under the microscope, a teratoma contains a mix of tissues that would not normally be found together. Pathologists group these tissues by the three layers of a developing baby that they come from.
In a mature teratoma, all of these tissues look fully developed. In an immature teratoma, some areas resemble tissue from a developing baby, the most important of which is immature neuroepithelium. It consists of crowded, dark blue cells that form small tubes and rosettes, and it normally develops into the brain.
Pathologists grade immature teratomas based on how much immature neuroepithelium they find, while mature teratomas are not graded. The CAP protocol uses three grades, which some reports group as low-grade and high-grade.
In adults, the grade of an immature teratoma strongly influences treatment, but in children grade matters less. In newborns, the grade does not predict whether the tumor will behave in a cancerous way. In older children, a higher grade is linked to a higher chance of the tumor growing back, especially if it was not completely removed. Most children with a completely removed immature teratoma of any grade are treated with surgery alone.
For a child with teratoma, whether the tumor contains yolk sac tumor is usually more important than the grade. Yolk sac tumor is the most common cancerous germ cell tumor in babies and children. It can grow as tiny areas inside a teratoma that are easy to miss without careful sampling.
Yolk sac tumor matters because it can spread to other parts of the body, unlike mature teratoma. When a teratoma grows back after surgery, especially in infants, the regrowth is often pure yolk sac tumor. That is why the pathologist examines multiple tumor samples and uses special stains to look for it. Your child’s report may describe yolk sac tumor in one of these ways:
A pure mature or immature teratoma usually does not produce AFP. A raised AFP that does not fall after surgery suggests yolk sac tumor may still be present. Newborns, however, normally have very high AFP levels that fall over the first year of life, reaching adult levels between about 8 and 12 months. For this reason, doctors always compare a baby’s AFP result with the normal range for the baby’s age.
The chance of finding yolk sac tumor rises with the age at which a teratoma is removed. In a 2024 international study of more than 3,400 children with sacrococcygeal teratoma, cancer was found in about 3% of tumors removed at 3 months of age. The figure rose to about 10% at 1 year and about 33% at 2 years.
Teratoma in children differs from teratoma in adults in several ways that affect what your child’s report means. Much of the information about teratoma describes adults and may not apply to children.
A sacrococcygeal teratoma grows at the base of the spine, in the area of the tailbone. It is the most common teratoma in newborn babies. Many are seen on an ultrasound before birth, and others are obvious at birth as a mass on the buttocks.
A large sacrococcygeal teratoma can have a rich blood supply that puts strain on the baby’s heart before birth. When one is found on ultrasound, a fetal medicine and pediatric surgery center usually monitors the pregnancy and plans the delivery. Some sacrococcygeal teratomas grow entirely inside the pelvis. These are often found later in infancy or childhood, sometimes when a child has constipation or trouble passing urine.
Doctors describe where a sacrococcygeal teratoma sits using the Altman classification. It is based on examination and imaging rather than the pathology report, but it often appears in a child’s records.
Types II and III are linked to a higher chance of the sacrococcygeal teratoma growing back. Type IV tumors are more often found at an older age, when the chance of yolk sac tumor is higher.
The operation for a sacrococcygeal teratoma removes the coccyx, or tailbone, together with the tumor. This does not mean the tumor has grown into the bone. The cells that a sacrococcygeal teratoma grows from sit at the tip of the coccyx, so leaving the coccyx behind can allow the tumor to return.
When a pathologist examines the cut edges of the tissue, called the margins, after a teratoma is removed. Complete removal is one of the most important factors in whether a teratoma will grow back. For teratomas outside the ovary and testicle, the CAP protocol reports margins in these ways:
For an ovarian teratoma, the report describes whether the tumor surface was intact or ruptured and whether tumor cells were found outside the ovary. More detail is in our article on immature ovarian teratoma.
When a teratoma in a child contains yolk sac tumor or another cancerous germ cell tumor, it is usually given a stage. Children’s germ cell tumors are staged with the Children’s Oncology Group (COG) system, which the current CAP protocol uses. The stage depends on how completely the tumor was removed and whether it has spread.
A pure mature or immature teratoma that was completely removed usually needs no treatment beyond surgery. Your child’s care team can explain whether they assigned a stage and what it means.
Most children with teratoma are cured by surgery. In the large Italian study, about 99% of children were alive several years after diagnosis. About 91% had no regrowth, new tumor, or other serious event during follow-up.
The chance of the teratoma growing back depends mainly on the type and on whether it was completely removed.
When a teratoma recurs, it may return as a teratoma or a yolk sac tumor. Regrowth as a yolk sac tumor usually raises AFP, which is why AFP is checked during follow-up. Girls who had an ovarian teratoma also have a small chance of a new teratoma in the other ovary years later.
Rarely, a teratoma grows during chemotherapy even though the cancerous germ cell tumor is responding, a condition called growing teratoma syndrome. The growing tissue is a mature teratoma, which does not respond to chemotherapy and is removed with surgery.
Once a pathologist has confirmed teratoma, the next steps depend on the type of teratoma, whether yolk sac tumor was found, and whether the tumor was completely removed. A pediatric surgeon and a pediatric oncologist usually lead care.
Follow-up after teratoma usually includes physical examinations, AFP blood tests, and imaging. After a sacrococcygeal teratoma, the exam often includes a rectal exam to feel for a mass in the pelvis that cannot be seen from the outside. In the Italian study, children were checked every three to four months for the first two years, then every six months until five years. Your child’s care team can explain the follow-up plan. Clinical trials for children with germ cell tumors are ongoing, and the team can tell you whether one is open to your child.
A large sacrococcygeal teratoma, especially one that extended into the pelvis, can affect the nerves and muscles in that area. For this reason, longer-term follow-up after a sacrococcygeal teratoma also checks bowel and bladder function as the child grows.