Gestational trophoblastic disease (GTD) is a rare cancer in women that can occur during pregnancy. It develops in the uterus when cancerous cells grow in the tissues that are formed following conception (the union of a sperm and egg), and usually becomes evident some 10 to 16 weeks after conception. These tissues, called the trophoblast, develop into the placenta. In GTD, this tissue continues to grow, but the fetus does not develop.
Examination of GTD tissue has shown that the tumor often develops from an abnormal number of chromosomes when the sperm and egg unite.
More than 80 percent of GTD cases are of the noncancerous variety. All forms of GTD can be treated, and in the great majority of cases the treatment results in a cure. Most women who have had a single incidence of GTD can go on to have normal pregnancies later.
Types of GTD
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Hydatidiform Mole
A hydatidiform mole (also called a "molar pregnancy") is a noncancerous form of GTD that arises when the sperm and egg join but do not develop into a fetus, forming a tissue that resembles grape-like cysts. Hydatidiform moles may be complete (containing no fetal tissue) or partial (containing some tissue from an abnormal fetus that fails to develop completely). These tumors rarely spread beyond the uterus to other parts of the body; a small percentage of them may develop into cancerous GTD.
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Chorioadenoma & Choriocarcinoma
Chorioadenoma and choriocarcinoma are cancerous forms of GTD. Chorioadenoma spreads locally within the muscular wall of the uterus; choriocarcinoma spreads more widely within the body. These types of GTD may have begun as a hydatidiform mole or from tissue that remains in the uterus following an abortion or childbirth.
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Placental-Site GTD
Placental-site GTD is a very rare form of the disease that arises in the uterus at the site where the placenta was attached. These tumors usually do not spread to other parts of the body, but they can sometimes penetrate the muscle layer of the uterus.
Hydatidiform moles occur in only 1 of 1,500 pregnancies in the United States. Choriocarcinomas are even less common, arising in only 1 of every 20,000-40,000 pregnancies. When GTD does occur, it is most commonly found in very young women (under age 17) and in older women (those in their 30s and 40s). For unknown reasons, GTD is more common in Asian countries (occurring in as many as 1 of 100 pregnancies).
