"IT, intermediate trophoblast; EPS, exaggerated placental site; PSTT, placental site trophoblastic tumor; PSN, placental site nodule; ETT, epithelioid trophoblastic ''Except in multinucleated IT cells.

cCyclin E staining is diffuse in ETT but only very focal in PSN and chorionic-type IT.

Table 2 Classification of GTD

Molar lesions Complete hydatidiform mole Partial hydatidiform mole Invasive mole

Nonmolar lesions Choriocarcinoma PSTT ETT

Nonneoplastic benign lesions Exaggerated placental site Placental site nodule

(EPS) and placental site nodule were classified as "unclassified GTD." Both lesions are benign and have a distinct histogenesis and morphological features that justify their separate designation. The third World Health Organization classification also includes epithelioid trophoblastic tumor (ETT), a recently described trophoblastic neoplasm distinct from choriocarcinoma and placental site trophoblastic tumor (PSTT). Based on morphological and immunophenotypic features (Table 1), nonmolar GTD can be related to the different subpopulations of trophoblast. Although, each lesion is a distinct entity, it is not unusual for a nonmolar trophoblastic lesion to display mixed histological features of choriocarcinoma, PSTT, and ETT, underscoring the plasticity of trophoblastic differentiation within these tumors (5,24).

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