This is a medical question of type : information 
 What is (are) Gestational Trophoblastic Disease ? 
 Key Points
                    - Gestational trophoblastic disease (GTD) is a group of rare diseases in which abnormal trophoblast cells grow inside the uterus after conception.    - Hydatidiform mole (HM) is the most common type of GTD.    - Gestational trophoblastic neoplasia (GTN) is a type of gestational trophoblastic disease (GTD) that is almost always malignant.          - Invasive moles     - Choriocarcinomas     - Placental-site trophoblastic tumors     - Epithelioid trophoblastic tumors        - Age and a previous molar pregnancy affect the risk of GTD.    - Signs of GTD include abnormal vaginal bleeding and a uterus that is larger than normal.     - Tests that examine the uterus are used to detect (find) and diagnose gestational trophoblastic disease.    - Certain factors affect prognosis (chance of recovery) and treatment options.
                
                
                    Gestational trophoblastic disease (GTD) is a group of rare diseases in which abnormal trophoblast cells grow inside the uterus after conception.
                    In gestational trophoblastic disease (GTD), a tumor develops inside the uterus from tissue that forms after conception (the joining of sperm and egg). This tissue is made of trophoblast cells and normally surrounds the fertilized egg in the uterus. Trophoblast cells help connect the fertilized egg to the wall of the uterus and form part of the placenta (the organ that passes nutrients from the mother to the fetus).   Sometimes there is a problem with the fertilized egg and trophoblast cells. Instead of a healthy fetus developing, a tumor forms. Until there are signs or symptoms of the tumor, the pregnancy will seem like a normal pregnancy.   Most GTD is benign (not cancer) and does not spread, but some types become malignant (cancer) and spread to nearby tissues or distant parts of the body.   Gestational trophoblastic disease (GTD) is a general term that includes different types of disease:         -  Hydatidiform Moles (HM)               - Complete HM.      - Partial HM.             - Gestational Trophoblastic Neoplasia (GTN)               -  Invasive moles.      -  Choriocarcinomas.      - Placental-site trophoblastic tumors (PSTT; very rare).      - Epithelioid trophoblastic tumors (ETT; even more rare).
                
                
                    Hydatidiform mole (HM) is the most common type of GTD.
                    HMs are slow-growing tumors that look like sacs of fluid. An HM is also called a molar pregnancy. The cause of hydatidiform moles is not known.   HMs may be complete or partial:         - A complete HM forms when sperm fertilizes an egg that does not contain the mothers DNA. The egg has DNA from the father and the cells that were meant to become the placenta are abnormal.    - A partial HM forms when sperm fertilizes a normal egg and there are two sets of DNA from the father in the fertilized egg. Only part of the fetus forms and the cells that were meant to become the placenta are abnormal.        Most hydatidiform moles are benign, but they sometimes become cancer. Having one or more of the following risk factors increases the risk that a hydatidiform mole will become cancer:         - A pregnancy before 20 or after 35 years of age.    - A very high level of beta human chorionic gonadotropin (-hCG), a hormone made by the body during pregnancy.    - A large tumor in the uterus.     - An ovarian cyst larger than 6 centimeters.     -  High blood pressure during pregnancy.    - An overactive thyroid gland (extra thyroid hormone is made).    - Severe nausea and vomiting during pregnancy.    - Trophoblastic cells in the blood, which may block small blood vessels.     - Serious blood clotting problems caused by the HM.
                
                
                    Gestational trophoblastic neoplasia (GTN) is a type of gestational trophoblastic disease (GTD) that is almost always malignant.
                    Gestational trophoblastic neoplasia (GTN) includes the following:     Invasive moles    Invasive moles are made up of trophoblast cells that grow into the muscle layer of the uterus. Invasive moles are more likely to grow and spread than a hydatidiform mole. Rarely, a complete or partial HM may become an invasive mole. Sometimes an invasive mole will disappear without treatment.       Choriocarcinomas    A choriocarcinoma is a malignant tumor that forms from trophoblast cells and spreads to the muscle layer of the uterus and nearby blood vessels. It may also spread to other parts of the body, such as the brain, lungs, liver, kidney, spleen, intestines, pelvis, or vagina. A choriocarcinoma is more likely to form in women who have had any of the following:            -  Molar pregnancy, especially with a complete hydatidiform mole.      - Normal pregnancy.     - Tubal pregnancy (the fertilized egg implants in the fallopian tube rather than the uterus).     - Miscarriage.              Placental-site trophoblastic tumors    A placental-site trophoblastic tumor (PSTT) is a rare type of gestational trophoblastic neoplasia that forms where the placenta attaches to the uterus. The tumor forms from trophoblast cells and spreads into the muscle of the uterus and into blood vessels. It may also spread to the lungs, pelvis, or lymph nodes. A PSTT grows very slowly and signs or symptoms may appear months or years after a normal pregnancy.        Epithelioid trophoblastic tumors    An epithelioid trophoblastic tumor (ETT) is a very rare type of gestational trophoblastic neoplasia that may be benign or malignant. When the tumor is malignant, it may spread to the lungs.