Problems and pitfalls in the histopathologic diagnosis of gestational trophoblastic lesions.

Proliferative lesions of gestational trophoblast pose problems of interpretation and pitfalls in differential diagnosis. Normally an actively proliferative and invasive tissue, healthy trophoblast shares cytologic features with malignant neoplasms. When trophoblastic hyperplasia accompanies macroscopic villous swelling, a diagnosis of hydatidiform mole (HM) is in order. Exuberant and atypical avillous trophoblast characterizes choriocarcinoma (CCA) and placental site trophoblastic tumor (PSTT). The distinction between them rests on the dimorphic composition of CCA as contrasted with the relative monomorphism of PSTT. Immunohistochemical studies contribute to the latter differential diagnosis. Unfortunately, two common conditions share morphologic features with the major lesions of gestational trophoblast. The hydropic abortus may resemble HM; the banal implantation site in normal early pregnancy and later spontaneous abortion may suggest either CCA or PSTT. Familiarity with the normal and benign variants of chorionic epithelium and thorough tissue sampling may be helpful in difficult cases. Ambiguous lesions that do not conform to conventional classification should be referred for consultation. A few, however, will not fit neatly into diagnostic categories. In such instances, a descriptive report and clear communication with the patient's physician provide the best current approach to clinical follow-up.