A gestational trophoblastic tumor (GTT) is a rare cancer that occurs in a woman's reproductive system. Cancer begins when normal cells change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
A GTT is most commonly the result of an abnormal pregnancy due to an abnormal combination of a sperm and an egg. In other cases, a GTT is a cancerous growth that begins from a normal placenta. The placenta is the organ that develops during pregnancy and connects the fetus (unborn baby) to the uterus, also called the womb.
There are three types of GTTs:
Hydatidiform mole. Also called a molar pregnancy, this type accounts for about 80% of all GTTs. There are two main types of molar pregnancy: a complete molar pregnancy and a partial molar pregnancy. A complete molar pregnancy begins when a sperm fertilizes an abnormal egg. Instead of forming an embryo, the tissue grows into a mound of cells that look like grape-like cysts; there is no evidence of normal fetal development.
Partial molar pregnancy begins with fertilization of an egg by two sperm. It has some of the features of a complete molar pregnancy, but also has some fetal development. The fetus has abnormal chromosomes and has no potential for survival.
Another type of molar pregnancy is invasive molar pregnancy, which most commonly begins from a complete molar pregnancy, but can also arise from a partial molar pregnancy. An invasive molar pregnancy may grow into the muscle layer of the uterus. Fewer than 15% of hydatidiform moles spread outside of the uterus.
Choriocarcinoma. This type of GTT may begin as a hydatidiform mole or from the placenta, whether through delivery of a baby, abortion (induced termination of a pregnancy), or miscarriage (uninduced termination of a pregnancy). Choriocarcinoma can spread outside of the uterus. About 5% of all GTTs are choriocarcinomas.
Placental-site trophoblastic disease. This rare type of GTT can start in the placenta.
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