PSTT can develop following a term delivery, non-molar abortion, or CHM. There are currently about 100 recorded cases of PSTT in the literature and so estimates of its true incidence may well be inaccurate. Nevertheless, PSTT is thought to constitute about 1% of all tro-phoblastic tumours (choriocarcinoma, invasive mole, and PSTT).
PSTTs are slow-growing, malignant tumours composed mainly of cytotrophoblast with very little syncytiotrophoblast, so producing little HCG. However, they often stain strongly for human placental lactogen (HPL) which helps to distinguish this tumour from carcino mas, sarcomas, exaggerated placental-site reaction, and placental nodule. The raised HPL may cause hyperprolactinaemia that can result in amenorrhoea and/or galactorrhoea. In most cases spread occurs by local infiltration with distant metastases occurring late via the lymphatics and blood.
The behaviour of PSTT is thus quite different from other forms of GTD and it is relatively chemo-resistant. The best management is hysterectomy when the disease is localized to the uterus. When metastatic disease is present, patients can respond and be apparently cured by multi-agent chemotherapy either alone or in combination with surgery.
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