We performed an immunohistochemical and flow cytometric study of the
formalin-fixed,
paraffin-embedded tissues of eight recent gestational
choriocarcinomas (CCs) and three
placental-site trophoblastic tumors (PSTTs). The follow-up period ranged from 1 to 144 months (mean, 74.3 months). In the CCs, which consisted predominantly of cytotrophoblasts and syncytiotrophoblasts intermingled with small amounts of intermediate trophoblasts, cytotrophoblasts were occasionally positive for beta-subunit
human chorionic gonadotropin (HCG) and syncytiotrophoblasts contained abundant HCG. Some intermediate trophoblasts were positive for HCG and many were positive for
human placental lactogen. In the three PSTTs, which were characterized by a monomorphic proliferation of intermediate trophoblasts, the
tumor cells were positive for
human placental lactogen and
placental alkaline phosphatase. The
tumors of two patients, including one fatal case, contained more
human placental lactogen-positive cells than HCG-positive cells, while the
tumor of the remaining patient, who had high serum HCG levels, showed a reversed staining pattern resembling that of CC; this patient has been alive without disease for 9 years. One CC patient and one PSTT patient died of multiple lung
metastases, despite
hysterectomy and multiagent
chemotherapy. All CCs and PSTTs had an exclusively diploid
DNA content, and there was no correlation among histopathologic and immunohistochemical features,
DNA ploidy, S-phase fraction, and clinical outcome for patients with these
tumors. These results suggest that there is a PSTT that immunohistochemically resembles CC and that flow cytometric and immunohistochemical analysis may not be effective tools to predict the
biologic behavior of malignant
trophoblastic tumors.