What is gestational trophoblastic disease?
Gestational trophoblastic disease (GTD) is a group of rare tumors that involve abnormal growth of cells inside a woman's uterus. GTD does not develop from cells of the uterus like cervical cancer or endometrial (uterine lining) cancer do. Instead, these tumors start in the cells that would normally develop into the placenta during pregnancy. (The term "gestational" refers to pregnancy.)
GTD begins in the layer of cells called the trophoblast that normally surrounds an embryo. (Tropho- means "nutrition," and -blast means "bud" or "early developmental cell.") Early in normal development, the cells of this layer form tiny, finger-like projections known as villi. These villi grow into the lining of the uterus. In time, the trophoblast layer develops into the placenta, the organ that protects and nourishes the growing fetus.
Most GTDs are benign (non cancerous) and they don't invade deeply into body tissues or spread to other parts of the body. But some are cancerous. Because not all of these tumors are cancerous, this group of tumors may be referred to as gestational trophoblastic disease, gestational trophoblastic tumors, or gestational trophoblastic neoplasia. (The wordneoplasia simply means "new growth.")
All forms of GTD can be treated. And in most cases the treatment produces a complete cure.
Types of gestational trophoblastic disease
The main types of gestational trophoblastic diseases are:
- Hydatidiform mole (complete or partial)
- Invasive mole
- Choriocarcinoma
- Placental-site trophoblastic tumor
Hydatidiform mole
The most common form of GTD is called a hydatidiform mole, also known as a molar pregnancy. It is made up of villi that have become swollen with fluid. The swollen villi grow in clusters that look like bunches of grapes. This is called a molar "pregnancy," but it is not possible for a normal baby to form. Hydatidiform moles are not cancerous, but they may develop into cancerous GTDs.
There are 2 types of hydatidiform moles: complete and partial.
A complete hydatidiform mole most often develops when either 1 or 2 sperm cells fertilize an "empty" egg cell (a cell that contains no nucleus or DNA). All the genetic material comes from the father's sperm cell. Therefore, there is no fetal tissue.
Surgery can totally remove most complete moles, but in as many as 1 in 5 women there will be some persistent molar tissue (see the section, "Persistent gestational trophoblastic disease" below). Most often this is an invasive mole, but in rare cases it is a choriocarcinoma, a malignant (cancerous) form of GTD. In either case it will require further treatment.
A partial hydatidiform mole develops when 2 sperm fertilize a normal egg. These tumors contain some fetal tissue, but this is often mixed in with the trophoblastic tissue. It is important to know that a viable (able to live) fetus is not being formed.
Partial moles are usually completely removed by surgery. Only a small number of women with partial moles need further treatment after initial surgery. Partial moles rarely develop into malignant GTD.
Persistent gestational trophoblastic disease is a term used to describe GTD that is not cured by initial surgery. Persistent GTD occurs when the hydatiform mole has grown from the surface layer of the uterus into the muscle layer below (called themyometrium). The surgery used to treat a hydatiform mole (called suction dilation and curettage, or D&C) involves scraping the inside of the uterus. This removes only the inner layer of the uterus (the endometrium) and cannot remove tumor that has grown into the muscular layer.
Most cases of persistent GTD are invasive moles, but in rare cases they are choriocarcinomas or placental site trophoblastic tumors (see below).
Invasive mole
An invasive mole (formerly known as chorioadenoma destruens) is a hydatidiform mole that has grown into the muscle layer of the uterus. Invasive moles can develop from either complete or partial moles, but complete moles become invasive much more often than do partial moles. Invasive moles develop in a little less than 1 out of 5 women who have had a complete mole removed. The risk of developing an invasive mole in these women increases if:
- There is a long time (more than 4 months) between the last menstrual period and treatment.
- The uterus has become very large.
- The woman is older than 40 years.
- The woman has had GTD in the past.
Because these moles have grown into the uterine muscle layer, they aren't completely removed during a D&C. Invasive moles can sometimes go away on their own, but most often more treatment is needed.
A tumor or mole that grows completely through the wall of the uterus may result in bleeding into the abdominal or pelvic cavity. This bleeding can be life threatening.
Sometimes after removing a complete hydatidiform mole, the tumor spreads (metastasizes) to other parts of the body, most often the lungs. This occurs about 4% of the time (or 1 in 25 cases).
Choriocarcinoma
Choriocarcinoma is a malignant form of GTD. It is much more likely than other types of GTD to grow quickly and spread to organs away from the uterus.
Choriocarcinoma most often develops from a complete hydatidiform mole, but it can also occur after a partial mole, a normal pregnancy, or a pregnancy that ends early (such as a miscarriage or an elective abortion).
Rarely, choriocarcinomas can develop that are not related to pregnancy. These can be found in areas other than the uterus, and can occur in both men and women. They may develop in the ovaries, testicles, chest, or abdomen. In these cases, choriocarcinoma is usually mixed with other types of cancer, forming a type of cancer called a mixed germ cell tumor. These tumors are not considered to be gestational (related to pregnancy) and are not discussed in this document. Non-gestational choriocarcinoma can be less responsive to chemotherapy and may have a less favorable prognosis (outlook) than gestational choriocarcinoma. For more information about these tumors, see our documents, Ovarian Cancer and Testicular Cancer.
Placental-site trophoblastic tumor
Placental-site trophoblastic tumor (PSTT) is a very rare form of GTD that develops where the placenta attaches to the lining of the uterus. This tumor most often develops after a normal pregnancy or abortion, but it may also develop after a complete or partial mole is removed.
Most PSTTs do not spread to other sites in the body. But these tumors have a tendency to grow into (invade) the muscle layer of the uterus.
Most forms of GTD are very sensitive to chemotherapy drugs, but PSTTs are not. Instead, they are treated with surgery, aimed at completely removing disease.
