CNS germinoma (brain germinoma)

A germinoma is a kind of germ cell tumor. Germ cells are cells in an unborn baby that later become sperm or eggs. Most germ cell tumors grow in the testicles or ovaries. When one forms in the brain or spinal cord, doctors call it a central nervous system (CNS) germ cell tumor.

CNS germ cell tumors are split into two main groups: germinomas and nongerminomatous germ cell tumors (NGGCTs). Germinoma is the most common type and has the best outlook. The two groups are treated very differently, so one of the care team’s first jobs is to tell them apart. A tumor that mixes germinoma with other germ cell types is grouped with the nongerminomatous tumors.

CNS germ cell tumors most often start near the pineal gland, a small gland deep in the middle of the brain (about 45 in 100). The next most common place is the suprasellar region, just above the pituitary gland (about 30 in 100). The pituitary controls many of the body’s hormones. About 5 to 10 in 100 people have tumors in both places at once, which is called bifocal. CNS germ cell tumors are found most often between ages 10 and 19 and more often in boys and men. In Western countries they make up 3 to 4 in every 100 brain tumors in children. In Japan and other Asian countries the share is higher, about 15 in 100.

The cause of most CNS germ cell tumors is not known. One idea is that, while a baby grows in the womb, some early germ cells travel to the wrong place and later turn into a tumor. A study of chemical tags on the tumors’ DNA (methylation) supports this idea. Another idea is that the tumor starts from an early embryo cell that escaped the normal signals that control growth.

Lab studies have found changes in the tumor cells, for example in a gene called KIT and in genes that pass growth signals inside the cell. Researchers are still working out what these changes mean.

Some patterns are known. Boys and men are affected more often. The gap is largest for tumors in the pineal region, which are found mostly in males. Rates also differ by background. In U.S. cancer registry data from 1992 to 2010, people aged 10 to 29 of Asian or Pacific Islander descent had two to three times the rate of white people. Germ cell tumors are the most common kind of brain tumor reported in people with Down syndrome. Case reports also link Klinefelter syndrome, in which a male has an extra X chromosome, with germ cell tumors outside the testicles, including some in the brain.

Symptoms depend on where the tumor is. A tumor above the pituitary often affects hormones first. The most common early sign is diabetes insipidus, which 70 to 90 in 100 people with a tumor there have. This is not sugar diabetes. The body cannot hold on to water, so a person is very thirsty and passes large amounts of clear urine, sometimes with bed-wetting. People can make up for it by drinking a lot, sometimes for months or years before the tumor is found. Later there may be slow growth, early or late puberty, and loss of vision as the tumor presses on the nerves to the eyes.

A tumor in the pineal region can block the flow of the fluid around the brain (cerebrospinal fluid). The fluid builds up, a problem called hydrocephalus, and raises the pressure inside the head. This causes headaches, nausea, vomiting and tiredness. Pineal tumors can also cause trouble looking up, double vision and changes in how the pupils react to light. These symptoms usually build over weeks to months.

Some signs are easy to miss, such as bed-wetting, loss of appetite, trouble with schoolwork or changes in mood or behavior. This can delay the diagnosis. Germinoma can spread through the fluid to other parts of the brain and spine, but it rarely spreads outside the brain and spinal cord.

Treatment often means several rounds of chemotherapy and then a course of radiation. The scans and tests done at diagnosis are repeated to see how well treatment is working. Care is usually led by a pediatric oncologist or a radiation oncologist. The team may also include a neurosurgeon, an endocrinologist (hormone doctor), an eye doctor, a rehabilitation specialist, a psychologist, a social worker and a fertility specialist.

Hormone problems are common and often last. When the tumor has caused diabetes insipidus or other pituitary hormone losses, these usually stay even after the tumor is gone. Hormone replacement is then needed long term. Low pituitary function can affect growth, puberty, energy, thyroid function and fertility, so hormone levels are checked regularly.

Radiation to the brain can affect thinking, learning and memory. It can also affect vision, and in rare cases it leads to a stroke or a second tumor years later. These late effects can happen in teens and young adults as well as children. Follow-up with MRI scans continues for years, and many families also use school support and testing of thinking and learning skills (neuropsychology testing).

No donor is involved in the usual treatment of a CNS germinoma. Most people are treated with chemotherapy and radiation and never need a stem cell transplant.

A transplant is used only for some germinomas that come back. The care team then gives high-dose chemotherapy, which also destroys the blood-forming cells in the bone marrow. Before that treatment, stem cells are collected from the patient’s own blood or bone marrow and frozen. Afterward they are thawed and given back through a vein, where they rebuild the blood cells. This is called stem cell rescue, or an autologous transplant. It uses the patient’s own cells, so no registry match is needed.

U.S. transplant guidelines from NMDP and ASTCT say this own-cell treatment may be considered when a germinoma comes back and responds again to chemotherapy. A donor (allogeneic) transplant is not a standard treatment. European transplant experts (EBMT, 2025) say donor transplants for children with solid tumors should be explored only in clinical trials. Joining a registry helps people with many other conditions who do need a donor.