Persistent trophoblastic disease and choriocarcinoma are both rare conditions. They belong to a group of conditions known as gestational trophoblastic disease (GTD).
Persistent trophoblastic disease (PTD)
PTD can occur after treatment to remove a molar pregnancy but some molar tissue is left in the womb and it grows to form a new tumour. In a molar pregnancy the fertilisation of the egg by the sperm goes wrong and creates abnormal cells or clusters of water filled sacs inside the womb.
Choriocarcinomas are extremely rare and develop from cells of the placenta. They happen after 1 in 50,000 pregnancies. They can occur some time after any type of pregnancy (including miscarriages or terminations). Choriocarcinoma is more likely to happen after a molar pregnancy.
What a risk factor is
A risk factor is anything that can increase your chance of developing a particular disease. Each condition has different risk factors.
Remember that having one or more risk factor doesn't mean that you will definitely get GTD. Most people who have one or more risk factor never have a GTD, and some people who have none of the risk factors do develop it.
These conditions are very rare and this information is only a guide to what might increase your risk.
Previous molar pregnancy
About 10 to 15 out of every 100 women (10 to 15%) who have had a complete molar pregnancy will go on to develop persistent trophoblastic disease, and will need treatment with chemotherapy. For women who have had a partial molar pregnancy the risk is only 1 in 100 women (1%).