Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Gestational Trophoblastic Disease ?
    ### Response:
    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.
    