Placental site trophoblastic tumor (PSTT) is a malignancy of placental trophoblastic cells. This disease seemingly involves cancer transformation of placental trophoblastic cells. In that respect it is very reminiscent of a non-trophoblastic cancer. Like a non-trophoblastic cancer it produces primarilly small quantities of the hCG free ß-subunit or the hyperglycosylated free ß-subunit. It does not produce high concentration of total hCG and hyperglycosylated hCG like choriocarcinoma and gestational trophoblastic neoplasm.
PSTT is best diagnosed by histology, by an expert placental pathologist (such as Robert J. Kurman MD of Johns Hopkins Medical Center) or by a specialist at the Brewer, New England or Charing Cross Trophoblast Disease Specialty Center. The only other method to specifically diagnose PSTT is to demonstrate that 30%-100% of the total hCG immunoreactivity in blood is due to hCG free ß-subunit. Unfortunately, labs only run the hCG free ß-subunit tests in the USA for Down syndrome screening. Under an patent agreement promoted by Johnson and Johnson Inc. they are not allowed to use this test for cancer measurements. The only centers that can measure hCG free ß-subunit are the USA hCG Reference Service and laboratories in Canada.
PSTT develops from trophoblastic cells in pregnancy or hydatidiform mole. Such a malignancy may occur months or even years after pregnancy or hydatidiform mole. This is a very slow growing malignancy and is usually very curable. Standard treatment is a hysterectomy to remove PSTT mass.