Overview

A gestational trophoblastic tumor (GTT) is a rare cancer that occurs in women. Cancer begins when normal cells begin to 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 organ that develops during pregnancy and connects the fetus [unborn baby] to the uterus).

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 the invasive molar pregnancy, which most commonly begins from a complete molar pregnancy, but can also arise from a partial molar pregnancy. Most hydatidiform moles do not spread outside of the uterus. In fewer than 15% of molar pregnancies, there is evidence of 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.

Statistics

Overall, GTTs are rare. In the United States, GTTs account for less than 1% of all gynecologic cancers. A hydatidiform mole may develop in one in 1,000 pregnancies and 15% these cases become malignant (cancerous). Choriocarcinoma is rare, occurring one pregnancy out of 40,000 in the United States. Molar pregnancies occur much more often in Asian and African countries than in the United States. GTTs are typically curable, especially if found early.

Cancer statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States, but the actual risk for a particular individual may differ. It is not possible to tell a woman how long she will live with a GTT. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Statistics source: American Cancer Society.

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