Gestational Trophoblastic Disease (GTD)
What is GTD?
Gestational trophoblastic disease (GTD) is the umbrella name given to a group of abnormalities that occur in pregnancy. Tumors grow inside a woman's uterus, starting with abnormal cells growing in the tissue that is to become the placenta. In a normal pregnancy the placenta is the organ that feeds the fetus during gestation and grows together with the baby, providing nutritional sustenance. A baby may or may not develop in the case of a GTD.
GTD originates in the layer of cells that normally surrounds an embryo, called the trophoblast. Tropho means nutrition and blast means bud or early developmental cell. In the early development of a normal pregnancy, the cells of the trophoblast form tiny, finger-like projections known as villi that grow into the lining of the uterus. Over time this lay of trophoblast changes and grows into the placenta.
The Types of GTD
Most GTDs are not malignant and they usually don't invade the tissues or spread to other parts of the body. However, some are cancerous. The good news is that all forms of GTD can be treated and in most cases, the prognosis is excellent as the treatment exacts a complete cure.
The primary types of gestational trophoblastic disease are:
· hydatidform mole (complete or partial)
· invasive mole
· placental-site trophoblastic tumor
Partial and Complete Moles
Known as a molar pregnancy, the most common form of GTD is the hydatidform mole which is made of villi that have become swollen with fluid. They grow in a form that resembles clusters of grapes. Although this is called a molar "pregnancy", it is impossible for a normal baby to take shape. While hydatidiform moles are not cancerous, it is possible for them to develop into malignancies.
Hydatidiform moles are either complete or partial. The complete mole happens most often when one or two sperm cells fertilize an empty egg - one that has no nucleus or DNA. Since all of the genetic material comes from the sperm, there is no fetal tissue formed. Complete moles can be totally removed with surgery, however, often there are remnants of molar tissue that can form into a carcinoma and will require further treatment.
A partial hydatidiform mole occurs when two sperm fertilize one egg. There is some fetal tissue in the tumor but it is mixed in with the trophoblastic tissue. A viable fetus cannot be properly formed in a case such as partial hydatidiform molar pregnancy. Partial moles are completely removed by surgery and very rarely do they develop into cancer. Persistent gestational trophoblastic disease is GTD that is not cured by surgery because the tumor has embedded in the muscular layer of the uterus. Most persistent GTDs are invasive moles, choriocarcinomas or placental site trophoblastic tumors.
Invasive Moles that Become Cancerous
An invasive mole is one that has grown into the muscle layer of the uterus. It can develop from a complete or a partial mole, however, complete moles tend to become invasive more than partial moles do. Invasive moles occur in about one in five women who have had a complete mole removed. They can disappear on their own, but more often than not, treatment is needed to rid the body of them entirely. Left alone, the invasive mole can metastasize and spread, most frequently to the lungs.
The malignant form of GTD is called choriocarcinoma and is the most likely of all GTDs to spread to organs outside of the uterus. Most often it develops from a complete hydatidiform mole, but it can also result from a partial mole, a normal pregnancy, or a pregnancy that ends in miscarriage or abortion.
The Rarest Form of GTD
The rarest form of GTD is called placental-site trophoblastic tumor (PSTT) and it grows where the placenta attaches to the uterine lining. This tumor most commonly develops after a normal pregnancy or after an abortion. However, it can also form after the removal of a partial or complete mole. Although most PSTTs do not spread within the body, they do tend to invade the walls of the uterus and unlike other GTDs the PSTT is not sensitive to chemotherapy drugs. As a result, they are best treated with surgery with a view to removing the disease completely.
Read our informative article on Molar Pregnancy here to learn more about this condition and who is most affected.