Gestational trophoblastic diseases: 3. Human chorionic gonadotropin-free β-subunit, a reliable marker of placental site trophoblastic tumors

Measurement of the proportion hCG-free β-subunit(%) was found to be useful in the diagnosis of PSTT using proposed cutoff values of >35% and >80%. While this finding needs to be confirmed by larger studies, it would be reasonable to measure hCG-free β-subunit(%) whenever the diagnosis of PSTT is considered.