Gestational Trophoblastic Disease: Overview

This section has been reviewed and approved by the Cancer.Net Editorial Board, 07/2014

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The uterus is a part of a woman’s reproductive system. It is pear-shaped, hollow, and located in a woman's pelvis between her bladder and rectum. The uterus is also known as the womb, where a fetus (unborn baby) grows when a woman is pregnant. It has three sections: the cervix, which is the narrow, lower section; the corpus, which is the broad, middle section; and the fundus, which is the dome-shaped top section. The uterine wall has two layers of tissue. The inner layer is called the endometrium, and the outer layer is muscle tissue called the myometrium.

About gestational trophoblastic disease

Gestational trophoblastic disease (GTD) is the general name for a group of rare tumors that occur during pregnancy in the fetal chorion, which is the outer part of the sac that surrounds the fetus as it grows. GTD can occur in any kind of pregnancy.  GTD is almost always curable, especially if found early.

This type of tumor begins when normal cells of the placenta, called trophoblast cells, change and form a mass. GTD is usually benign, which means noncancerous. But some GTD tumors can be cancerous, meaning they can spread to other parts of the body.

Usually, GTD occurs when there is a problem during the combination of a man’s sperm and a woman’s egg. Trophoblast cells normally grow and surround a fertilized egg in the uterus, helping to connect the fertilized egg to the uterine wall and to form the placenta. The placenta is the organ that develops during pregnancy to provide nutrients to the fetus from the mother. When this type of problem occurs, a healthy fetus will not develop and a tumor forms instead. In rare cases, GTD is a cancerous growth that begins from a normal placenta and may be found after a normal pregnancy and delivery of a baby.

Types of GTD

There are two main groupings of GTD. The first group is called hydatidiform moles, and the second group is called gestational trophoblastic neoplasia. There are subtypes under each grouping, explained below.

Hydatidiform Moles (HM). HMs account for about 80% of all GTD. A hydatidiform mole is also called a molar pregnancy. There are two types of HM: complete or partial. HMs are usually slow-growing and benign, although there is a chance a mole can become cancerous. A complete HM is much more likely to become cancerous than a partial HM.

A complete HM begins when sperm fertilizes an abnormal egg that doesn’t contain the mother’s DNA or a nucleus. Instead of forming a fetus, the tissue grows into a mound of cells that look like grape-like cysts.

A partial HM begins with fertilization of a normal egg by two sperm, so there are two sets of DNA from the father. The result has some of the features of a complete HM but part of the fetus may form, although there is no chance for fetal survival.

Gestational Trophoblastic Neoplasia (GTN). The second grouping is called GTN. While they can be related to HMs, GTNs are typically cancerous. The main types of GTNs include:

Invasive mole. Although it is also a type of HM, an invasive mole is considered a GTN because of its potential to grow and spread. An invasive mole may grow into the muscle layer of the woman’s uterus. Fewer than 15% of HMs spread outside of the uterus.

Choriocarcinoma. This is a cancerous tumor formed from trophoblast cells, and it can grow and spread more quickly than other GTNs. Choriocarcinoma can spread to the uterine muscle layer, nearby blood vessels, and outside of the uterus, including to nearby organs, brain, lung, liver, or kidneys. About 5% of all GTD are choriocarcinomas. It is most often found in women who’ve had an HM; a normal pregnancy and delivery of a baby; a tubal pregnancy where the fetus grows in the fallopian tube instead of the uterus; an induced ending of a pregnancy called an abortion; or an uninduced ending of a pregnancy called a miscarriage.

Placental-site trophoblastic tumor (PSTT). This rare type of GTN is also formed from trophoblast cells. It starts where the placenta joins with the uterus. This type of tumor grows slowly, but it can eventually spread to the uterine muscle, nearby blood vessels, or to the lymph nodes, pelvis, or lungs. Signs and symptoms may not occur until well after a normal pregnancy, an abortion, or treatment for an HM.

Epithelioid trophoblastic tumor (ETT). This is an extremely rare type of GTD. If it does spread, the most common area is the lungs. It is most often found after a normal pregnancy. ETT can also take a long time to show signs and symptoms.

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