Hydatidiform moles occur in about 1 pregnancy out of 1,000 in the United States and Europe. In very rare cases (less than 1%), a normal fetus can develop along with the hydatidiform mole.
In about 15% of cases, a hydatidiform mole will progress to become an "invasive" mole. Overall, invasive moles occur at an estimated rate of 1 pregnancy in 15,000.
Choriocarcinoma, a malignant form of gestational trophoblastic disease (GTD), is even less common, affecting approximately 1 pregnancy out of 40,000 in the United States. Like other forms of GTD, choriocarcinoma is more common in many Asian and African countries.
About 2% to 4% of hydatidiform moles progress to become choriocarcinoma. But only half of all gestational choriocarcinomas start off as molar pregnancies. About one-quarter of all choriocarcinomas develop in women who have a miscarriage (spontaneous abortion), intentional abortion, or tubal pregnancy (the fetus develops in the fallopian tube, rather than in the uterus). Another one-quarter occur after normal pregnancy and delivery.
Overall, gestational trophoblastic tumors account for less than 1% of female reproductive system cancers.
Cure rates depend on the type of GTD and its stage, as described in the section “Treatment of GTD by type and stage.”
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