Placental site trophoblastic tumor (PSTT): a case report and review of the literature

Abstract

Placental site trophoblastic tumor (PSTT), also known as atypical choriocarcinoma, syncytioma, chorioepitheliosis or trophoblastic pseudotumor, is a rare gestational trophoblastic disease (0.25-5% of all trophoblastic tumors) and it is composed by neoplastic proliferation of intermediate trophoblasts at placental implantation site. It consists of aggregates or sheets of large, polyhedral to round, predominantly mononucleated cells with a characteristic vascular and myometrial invasion. Main differential diagnoses are gestational choriocarcinoma (GC) and epitelioid trophoblastic tumor (ETT). We present a case of PSTT in a 25-year-old woman. Neoplastic cells showed moderate/high nuclear pleomorphism, abundant amphophilic, eosinophilic and clear cytoplasm, numerous mitotic figures (10 mitoses/10 HPF), and myometrial invasion. Other features are necrosis, vascular invasion with replacement of myometrial vessels by tumor cells and hemorrhage. The patient showed typical low serum β-hCG levels and high serum humane placental lactogen (hPL) levels.

Keywords: HPL; Intermediate trophoblast; gestational trophoblastic disease; placental site trophoblastic tumor.

Figure 1.

(A-B) Opened hysterectomy specimen containing placental site trophoblastic tumor (PSTT). The cut surface shows a pale-tan fleshy and hemorrhagic mass arising from the endomyometrium.

Figure 2.

(A-D) Microscopic analysis reveals coagulative tumor cell necrosis (A), hemorrhagic areas (B), neoplastic intermediate trophoblasts infiltrating myometrium by separating individual muscle fibers (C) and vascular invasion with replacement of myometrial vessels by tumor cells (D).

Figure 3.

(A-D) Vascular invasion pattern recapitulates that of normal implantation trophoblast: the tumor cells replace the wall of myometrial vessels and these transformed blood vessels allowed PSTT diagnosis (A,B). At higher magnification, there is a cellular proliferation of neoplastic intermediate trophoblast cells, characterized by abundant amphophilic, eosinophilic or clear cytoplasm, variable nuclear size and shape with marked hypercromasia, nuclear grooves, pseudoinclusions, prominent nucleoli and several mitoses (green arrowhead) (C,D).

Figure 4.

(A-D) Immunohistochemical profile shows a high proliferative index (Ki-67>30%) (A,B) and diffuse and strong cytoplasm staining for hPL confirming PSTT diagnosis (C,D).