Risks and causes of invasive mole and choriocarcinoma

A risk factor is anything that can increase your risk of developing a disease. Each condition has different risk factors.

Previous molar pregnancy

The main known risk factor for invasive mole and choriocarcinoma is a previous molar pregnancy. But invasive mole and choriocarcinoma are very rare. The number of women who develop one of these conditions following a molar pregnancy is small.

A molar pregnancy occurs when the fertilisation of the egg by the sperm goes wrong. This leads to the growth of abnormal cells or clusters of water filled sacs inside the womb. Usually any molar cells left after treatment will die off by themselves. But sometimes they will keep growing and become cancerous. This is called an invasive mole or persistent trophoblastic disease (PTD).

About 13 to 16 out of every 100 women (about 13 to 16%) who have had a complete molar pregnancy will go on to develop an invasive mole. For women who have had a partial molar pregnancy, the risk is only 1 in 100 women (1%). 

Choriocarcinomas are extremely rare cancers. They are more likely to develop after a molar pregnancy. But they can also happen following a full term pregnancy, miscarriage, ectopic pregnancy or abortion.

Researchers aren’t completely sure what causes molar pregnancies. But we do know of some factors that increase a woman's risk of developing one.