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

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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.

Original languageEnglish (US)
Pages (from-to)27-33
Number of pages7
JournalHuman pathology
Issue number1
StatePublished - Jan 1 1998



  • Choriocarcinoma
  • Exaggerated placental site
  • Ki-67
  • Mel-CAM
  • Placenta
  • Placental site trophoblastic tumor
  • Proliferation
  • Trophoblast

ASJC Scopus subject areas

  • Pathology and Forensic Medicine

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