THE PLACENTAL SITE NODULE - AN IMMUNOHISTOCHEMICAL STUDY

The placental site nodule and plaque (PSN-P) is a recently described, benign proliferation of intermediate trophoblast cells (ITs) in the en dometrium or endocervix occurring after an intrauterine gestation. We performed an extensive immunohistochemical study of 11 cases of PSN-P. Cytokeratins (AE1/AE3 and MAK 6) were strongly positive in all cases stained. Epithelial membrane antigen (EMA) was positive in all cases, in 5% to 75% of lesional cells. Expression of human placental lactogen (hPL) was weak and focal, and a minority of cases were positive for h uman chorionic gonadotropin (hCG). More help ful in identifying the tr ophoblastic nature of the lesion was pregnancy-specific beta-1 glycopr otein (SP1), which was present in 100% of cases, and placental alkalin e phosphatase (FLAP), present at least focally in 90% of cases stained . Vimentin was strongly positive in all cases stained. The presence of vimentin, SP1, and FLAP in PSN-P has not been documented previously. In our opinion cytokeratin, vimentin, and SP-l are the most important monoclonal antibodies to aid in the differential diagnosis of PSN-P. C opyright (C) 1994 by W.B. Saunders Company