title: Ki-67 labeling index in the differential diagnosis of exaggerated placental site, placental site trophoblastic tumor, and choriocarcinoma: a double immunohistochemical staining technique using Ki-67 and Mel-CAM antibodies.
abstract: The diagnosis of placental site trophoblastic lesions, particularly the distinction of a placental site trophoblastic tumor from an exaggerated placental site, can be difficult. Mel-CAM (also known as CD146 and MUC18) is a recently recognized cell adhesion molecule belonging to the immunoglobin gene superfamily that specifically identifies intermediate trophoblast (IT). In this study, we evaluated immunohistochemical staining of Ki-67 (using Mib-1 antibody) in Mel-CAM defined IT as an aid in the differential diagnosis of these lesions. Formalin-fixed tissue samples from 24 normal implantation sites, 19 exaggerated placental sites, five molar implantation sites, 16 placental site trophoblastic tumors, and 12 choriocarcinomas were stained with a Mel-CAM-specific polyclonal antibody and a Ki-67 antibody using streptavidin-biotin immunoperoxidase with two different chromagens. No Ki-67 nuclear labeling was seen in IT of normal implantation sites. The Ki-67 index (mean +/- standard deviation) in IT of exaggerated placental site was near zero, but in the molar implantation sites the Ki-67 index was 5.2% +/- 4.0%. In contrast, the Ki-67 index in IT of placental site trophoblastic tumor was 14% +/- 6.9% and in choriocarcinoma was 69% +/- 20%. The differences in the Ki-67 labeling index were statistically significant (P < .001) between exaggerated placental site, placental site trophoblastic tumor, and choriocarcinoma. In conclusion, a double-staining technique using MIB-1 antibody to determine the Ki-67 proliferative index in Mel-CAM defined IT is a useful technique in the differential diagnosis of exaggerated placental site versus placental site trophoblastic tumor and placental site trophoblastic tumor versus choriocarcinoma.
authors.affiliation: Department of Pathology, John Hopkins University School of Medicine, Baltimore, MD 21287-6917, USA.
authors.forename: I M
authors.initials: IM
authors.lastname: Shih
authors.forename: R J
authors.initials: RJ
authors.lastname: Kurman
mesh_terms: D015703:Antigens, CD; D014408:Biomarkers, Tumor / Q000032:analysis; D051929:CD146 Antigen; D002822:Choriocarcinoma / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods*; D019394:Ki-67 Antigen / Q000032:analysis*; D008562:Membrane Glycoproteins / Q000032:analysis; D008940:Mitotic Index; D019006:Neural Cell Adhesion Molecules; D010920:Placenta / Q000473:pathology; D011247:Pregnancy; D018245:Trophoblastic Tumor, Placental Site / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology; D014327:Trophoblasts / Q000473:pathology; D014594:Uterine Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology
chemical_list: D015703:Antigens, CD; D014408:Biomarkers, Tumor; D051929:CD146 Antigen; D019394:Ki-67 Antigen; C497902:MCAM protein, human; D008562:Membrane Glycoproteins; D019006:Neural Cell Adhesion Molecules