germ cell tumor
Meaning of germ cell tumor: Tumors of the cells that make eggs and sperm, which is why they appear in the chest and brain as well as the gonads.
Definition of germ cell tumor
A germ cell tumor is a growth arising from the cells that would otherwise become eggs or sperm. Most occur in the ovary or testis, but because these cells migrate through the embryo before settling in the gonads, tumors also appear along that midline path in the chest, the abdomen, the tailbone and the brain. They may be benign or malignant.
Why do they appear outside the gonads?
The answer lies in early development. Germ cell precursors form near the yolk sac and then crawl along the midline of the embryo to reach the developing ovary or testis. A few stall on the way. Those strays keep the capacities of the cells they came from, so a tumor arising from one can appear anywhere along that route: the tailbone in newborns, the chest between the lungs in young adults, the back of the abdomen, or the pineal region of the brain. Such a growth is an extragonadal germ cell tumor, and its midline position is the clue to its origin.
What types are there?
| Type | Behavior | Marker often raised |
|---|---|---|
| Seminoma or dysgerminoma | Slower growing, highly sensitive to radiation | hCG in some cases, never AFP |
| Yolk sac tumor | Malignant, frequent in children | AFP |
| Choriocarcinoma | Aggressive, spreads early through the blood | hCG, often markedly |
| Embryonal carcinoma | Malignant, usually mixed with other types | Variable |
| Teratoma | Contains tissue such as hair, skin or teeth | Usually none |
Mixtures are the rule rather than the exception, and one tumor can hold several of these components at once, which is why the whole specimen is examined rather than a single block of it.
Why do blood markers matter so much?
Few cancers release substances into the blood as reliably as these do. Alpha fetoprotein and the pregnancy hormone hCG come from specific components, so a level measured before treatment provides a baseline against which response is judged, and a level that fails to fall as expected points to disease still present. The markers also correct the label: a growth that looks like pure seminoma under the microscope but raises alpha fetoprotein is treated as though it holds another component, because seminoma cells do not make that protein.
How treatable are they?
Better than almost any other group of solid cancers, including when they have spread. The malignant forms respond strongly to platinum based chemotherapy, and cure remains achievable in advanced disease. Mature teratoma is the exception in the opposite direction: it does not respond to chemotherapy at all, because its cells are not dividing quickly, so any mass left behind is removed surgically instead.
Also known as
Used in a sentence
Tumor markers were repeated after surgery for a mixed germ cell tumor.
Good to know
Seminoma cells do not produce alpha fetoprotein, so a raised level in a tumor that appears to be pure seminoma indicates another component and changes how the tumor is managed.
Word origin
Where “germ cell tumor” comes from
Germ comes from the Latin germen, meaning a sprout or bud; tumor from tumere, meaning to swell.