Placental Site Trophoblastic Tumour (PSTT)

PSTT is a rare form of gestational trophoblastic disease (GTD) arising from intermediate trophoblast cells at the placental implantation site. Its biology differs markedly from choriocarcinoma, which explains its distinctive hormonal, histological, and treatment-response profile. The correct answer is option 4 (Statements 1, 2 and 4).

Evaluating Each Statement

• Statement 1 — Low serum β-hCG (Correct): Since PSTT is composed predominantly of intermediate trophoblast with only scattered syncytiotrophoblastic cells (the main source of β-hCG), serum β-hCG levels are disproportionately low relative to the tumour bulk. This is a classic distinguishing feature from choriocarcinoma, which produces very high β-hCG. Human placental lactogen (hPL) is often a more useful marker in PSTT.
• Statement 2 — Composed mainly of cytotrophoblast-lineage intermediate trophoblast (Correct): PSTT arises from and is composed chiefly of intermediate/cytotrophoblastic-type trophoblast cells (rather than syncytiotrophoblast), which infiltrate the myometrium and vasculature in a pattern resembling normal implantation-site trophoblast, but in an exaggerated and neoplastic fashion.
• Statement 3 — Highly responsive to chemoradiation (Incorrect): Unlike choriocarcinoma, PSTT is characteristically relatively resistant to chemotherapy and radiotherapy. Because of this poor chemosensitivity, the mainstay of treatment for localized disease is surgical hysterectomy, with chemotherapy reserved mainly for metastatic or high-risk disease.
• Statement 4 — Local invasion into myometrium (Correct): PSTT is well known for deep, exaggerated local invasion into the myometrium and adjacent vasculature, mimicking the normal deep implantation of trophoblast but in a tumorous, space-occupying manner. This local invasiveness is a hallmark diagnostic feature, though distant metastasis is uncommon compared to choriocarcinoma.

Conclusion

Statements 1, 2, and 4 accurately describe PSTT, while Statement 3 is false because PSTT is comparatively chemoresistant, making surgery the primary treatment. Hence, the correct combination is 1, 2 and 4.