What is Gestational Trophoblastic Disease

Executive Summary

Gestational Trophoblastic Disease is a rare disease that is a result of a group of tumors that develop during abnormal pregnancies, starting in the womb and forming the cells that are typically produced in the placenta. It mainly affects the uterus and can occur during pregnancy and is almost always curable if found early. It is usually benign and appears when there is some problem during the combination of the sperm and the egg in the uterus. There are two types of gestational trophoblastic disease that are prevalent: molar pregnancy (hydatidiform moles) and the second group being gestational trophoblastic neoplasia. The various subtypes of each grouping include Molar pregnancy (hydatidiform moles) that accounts for 80% of all GTD involving complete or partial molar pregnancy. The gestational trophoblastic neoplasia has an invasive mole, choriocarcinoma, placental-site trophoblastic tumor (PSTT), and epithelioid trophoblastic tumor (ETT).

What is Gestational Trophoblastic Disease?

A gestational trophoblastic disease is a group of tumors that forms during abnormal pregnancies that start in the womb and form the cells that typically develop into the placenta ^​1​. These are extremely rare.

The gestational trophoblastic disease affects the uterus. The uterus is a vital part of the female reproductive system and has two sections: the cervix, the narrow, lower section, and the corpus, which is the broad and middle section. The fundus is a dome-shaped top section of the corpus. The uterine wall has two tissue layers. The inner layer is the endometrium. The outer layer is the myometrium. 

About Gestational Trophoblastic Disease

GTD is the generalized name for a group of rare tumors during pregnancy in the fetal chorion, which is the outer part of the sac that surrounds the fetus as it grows ^​2​. GTD can occur during any pregnancy and is almost always curable, primarily 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. Some GTD tumors can be cancerous, called malignant, meaning they can spread to other body parts.

Usually, GTD occurs when there is some problem during the combination of the sperm and the egg in the uterus. Trophoblast cells grow generally and surround a fertilized egg in the uterus, helping to attach the fertilized egg to the uterine wall and to form the placenta. But when this kind of problem occurs in the placental tissue, a healthy fetus usually doesn’t develop. Rarely, GTD is a cancerous growth that begins from a normal placenta, and it may be found after a normal pregnancy and the birth of a baby.

Types of Gestational Trophoblastic Disease

There are two leading groups of GTD ^​3​. The first group is molar pregnancy, also known as hydatidiform moles. The second group is known as gestational trophoblastic neoplasia (GTN). There are subtypes under each grouping that are explained below.

• Molar pregnancy (hydatidiform moles) accounts for about 80% of all GTD. There are two types of molar pregnancy – complete or partial. They are usually slow-growing and benign, although there is a chance a mole can become cancerous. A complete molar pregnancy is more likely to become cancerous than a partial molar pregnancy.
• A complete molar pregnancy begins when the sperm fertilizes an abnormal egg containing the mother’s DNA or nucleus. There is no chance that a healthy baby will develop. Instead of forming a fetus, the tissue grows into a mound of cells that look like grape-shaped cysts. This may also be known as a complete hydatidiform mole.
• A partial molar pregnancy begins with fertilizing a regular egg with two sperm, so the father has two sets of DNA. The result has some features of complete molar pregnancy, and part of the fetus may form, but there are no chances that a healthy baby will develop. This may also be called a partial hydatidiform mole.

GTN

While GTNs can be related to a molar pregnancy, they are typically cancerous. This means they can spread to other body parts. The main types of GTNs include-

• Invasive mole –  Although an invasive mole is a type of molar pregnancy, it is considered a GTN because of its potential to grow and spread. An invasive mole may extend into the muscular layer of the uterus. Fewer than 15% of molar pregnancies turn invasive and lay outside the uterus.
• Choriocarcinoma – This is a cancerous tumor formed from trophoblast cells. It can grow and spread more quickly than other GTNs. Choriocarcinoma can spread to the uterine muscular layer, nearby blood vessels, and outside the uterus to nearby organs or distant organs, like the brain, lungs, liver, or kidneys. Around 5% of all GTD is choriocarcinoma. It is mostly found in women who have had a molar pregnancy. Seldom, choriocarcinoma occurs after a normal pregnancy, abortion, or tubal pregnancy, when the fetus grows in the fallopian tube instead of the uterus.
• A placental-site trophoblastic tumor (PSTT) – This rare type of GTN is also formed from trophoblast cells. It begins 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, lymph nodes, pelvis, or lungs. Symptoms and signs may not occur until well after a normal pregnancy, an abortion, or treatment for a molar pregnancy.

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

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