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Gestational trophoblastic disease (GTD)

What is Gestational trophoblastic disease?

Gestational trophoblastic disease includes any of a group of tumours that develops from trophoblastic cells (cells that help an embryo attach to the uterus and help form the placenta) after fertilisation of an egg by a sperm.

Gestational trophoblastic disease is also called gestational trophoblastic tumour.

The types of gestational trophoblastic disease are hydatidiform mole (also called a molar pregnancy), gestational trophoblastic neoplasia and placental-site trophoblastic tumour.

A hydatidiform mole is usually benign (not cancer) but it may spread to nearby tissues (invasive mole) or become a malignant tumour.

Gestational trophoblastic disease occurs in women during the years when they are able to have children.

The female reproductive organs

Gestational trophoblastic disease starts inside the uterus, the hollow, muscular, pear-shaped organ (also called the womb) where a baby grows.

The uterus is the main female reproductive organ. The bulk of the uterus is smooth muscle tissue, which is called the myometrium. The uterus sits low in the abdomen between the bladder and rectum and is held there lightly by muscle. It is joined to the vagina by the cervix, which is the neck of the uterus.

When women ovulate, or produce eggs in their ovaries, an egg travels through their fallopian tube into the uterus. If the egg is fertilised by a sperm, it will implant itself into the lining of the uterus and grow into a baby.

The lining of the uterus is called the endometrium. The endometrium is made up of several layers, including skin-like cells (surface epithelium), blood vessels, tissue spaces and glands. If a woman is ovulating, the endometrium will grow thicker each month to prepare for pregnancy. If the egg is not fertilised, the top layers of the endometrium are shed and flow out of the body through the vagina during menstruation. This is known as a woman’s period.

What is cancer?

Cancer is a group of many related diseases. All cancers begin in cells, the body’s basic building blocks.

Normally, cells grow and multiply in an orderly way.

However, damaged genes can cause them to behave abnormally. They may grow into a lump called a tumour. Tumours can be benign (not cancer) or malignant (cancer).

A malignant tumour is made up of cancer cells. If these cells are not treated, they may spread beyond their normal boundaries and into surrounding tissues, becoming invasive cancer. This spread of cancer is called metastasis.

When cancer spreads from its original place to another part of the body, the new tumour has the same kind of abnormal cells and the same name as the primary tumour.

Types of gestational trophoblastic disease

The types of gestational trophoblastic disease include hydatidiform mole, gestational trophoblastic neoplasia and placental-site trophoblastic tumour.

  • Hydatidiform mole. If a woman has a hydatidiform mole (also called a molar pregnancy), the sperm and egg cells have joined without the development of a baby in the uterus. Instead, the tissue that is formed resembles grape-like cysts.
    A hydatidiform mole is usually benign (not cancer) but it may spread to nearby tissues (invasive mole) or become a malignant tumour called gestational trophoblastic neoplasia. Hydatidiform mole is the most common type of gestational trophoblastic disease.
    There are two types of hydatidiform mole: complete and partial. In a complete hydatidiform mole, there is a mass of rapidly growing abnormal cells but no foetus. In a partial hydatidiform mole, there is an abnormal non-viable foetus and placenta. The two types also differ in their genetic makeup.
  • Gestational trophoblastic neoplasia. If a woman has gestational trophoblastic neoplasia, the tumour may have started from a hydatidiform mole, or from tissue that remains in the uterus following an abortion or delivery of baby. Gestational trophoblastic neoplasia can spread from the uterus to other parts of the body.
  • Placental-site trophoblastic tumour. This is a very rare type of gestational trophoblastic tumour that starts in the uterus where the placenta was attached.

How common is gestational trophoblastic disease?

Gestational trophoblastic disease is rare.

In Australia, hydatidiform moles occur in about one in 1,500 pregnancies.

Gestational trophoblastic neoplasia and placental-site trophoblastic tumours are even less common. Placental-site trophoblastic tumours are diagnosed in about seven Australian women each year.