Types of gestational trophoblastic disease

There are 2 main groups of gestational trophoblastic disease (GTD). The groups are hydatidiform moles and gestational trophoblastic neoplasms. All types of GTD produce human chorionic gonadotropin (HCG or b-HCG), which is a hormone that is found during pregnancy. It is normally found in the blood and urine of pregnant women.

A hydatidiform mole is the most common type of GTD. It is usually a non-cancerous tumour, but there is a chance that it can persist after removal and spread. A hydatidiform mole may also be called a molar pregnancy. This is not a normal pregnancy because a normal fetus does not form. A hydatidiform mole is made up of many swollen and fluid-filled deteriorated chorionic villi.

In rare cases, a normal fetus can develop alongside the hydatidiform mole. In these cases, the hydatidiform mole is treated after the baby is born.

There are 2 types of hydatidiform moles.

A complete hydatidiform mole develops when there is a total loss of the mother’s DNA after fertilization and a doubling of the father’s DNA. No fetus forms because all of the genetic information is from the father’s sperm. Instead of forming a fetus, the tissue grows to look like a cluster of grapes.

A partial hydatidiform mole usually develops when a normal egg is fertilized by 2 sperm. The tumour contains a mixture of fetal and abnormal trophoblast tissue. If there is a fetus, it usually is abnormal and cannot develop normally. These tumours have a lower risk of persisting after treatment or developing into cancer than complete hydatidiform moles.

Gestational trophoblastic neoplasia (GTN) can be related to hydatidiform moles but are almost always cancerous. There are several types of GTN.

An invasive mole occurs when a hydatidiform mole grows into the muscle wall of the uterus (myometrium). They can occur in less than 1 in 5 women who have had a complete mole removed.

Invasive moles are cancerous but they usually do not spread outside of the uterus. Complete hydatidiform moles are more likely than partial moles to become an invasive mole. Invasive moles can cause serious bleeding if they grow through the muscle wall of the uterus.

Gestational choriocarcinoma usually develops following a hydatidiform mole, but sometimes it develops after a miscarriage (spontaneous abortion), an elective abortion (when a woman chooses to terminate a pregnancy), a tubal (ectopic) pregnancy or a normal pregnancy. Gestational choriocarcinoma is an aggressive tumour that can grow very quickly and easily spread to other parts of the body.

In rare cases, a choriocarcinoma that is not related to pregnancy spontaneously develops in the ovaries (in women), the testicles (in men) or the abdomen. This type of tumour may be called non-gestational choriocarcinoma.

Placental site trophoblastic tumour is a very rare form of GTN. It starts from specialized cells in the placenta.

Most placental site trophoblastic tumours develop after a normal pregnancy, but they can also occur after a miscarriage, an elective abortion or the removal of a hydatidiform mole. Most placental site trophoblastic tumours don’t spread to other parts of the body but can grow into the muscle wall of the uterus.

An epithelioid trophoblastic tumour is extremely rare and most often develops after a normal pregnancy. Signs and symptoms can take a long time to appear because the tumour can take several years to develop. It can sometimes be found growing in the cervix. There may be distant metastases at the time of diagnosis.