Placental site trophoblastic tumor: Human placental lactogen and pregnancy-associated major basic protein as immunohistologic markers
Placental site trophoblastic tumor (PSTT) consists of a neoplastic proliferation of intermediate or extravillous trophoblast (also known as X cells). Pregnancy-associated major basic protein (pMBP) is a marker for placental intermediate trophoblast. We compared the distribution of pMBP and human placental lactogen (hPL) in 24 PSTT and 3 exaggerated placental site (EPS) specimens using two distinct immunohistologic methods. Statistical analyses were used to compare staining intensities in metastatic and nonmetastatic lesions. By immunofluorescence, 77% of the PSTT specimens and 100% of the EPS specimens stained with antibodies to pMBP, and the pMBP was localized in intermediate trophoblast and surrounding extracellular areas. By immunohistochemistry, 78% of the PSTT specimens and 100% of the EPS specimens stained for pMBP with a pattern comparable with that of immunofluorescence. Likewise, by immunohistochemistry, hPL stained 96% of the PSTT specimens and 100% of the EPS specimens. Immunohistochemical staining intensities for pMBP and hPL correlated (r2 = +.24; P = .013), but hPL staining was mainly confined to intermediate trophoblast and was more intense. Anti-pMBP tended to stain metastatic PSTT weakly. Thus, pMBP is a useful marker for intermediate trophoblast tumors and could help distinguish these from other forms of trophoblastic disease.