Malignant trophoblastic tumors: immunohistochemical and flow cytometric comparison of choriocarcinoma and placental site trophoblastic tumors.

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.