Malignant placental site trophoblastic tumor: a cytogenetic study using comparative genomic hybridization and chromosome in situ hybridization

BACKGROUND: Placental site trophoblastic tumor (PSTT) is a rare form of gestational trophoblastic neoplasm composed predominantly of intermediate trophoblast. Most showed benign behavior whereas 10-15% of PSTTs were clinically malignant with later recurrence and metastasis. Currently, there are no reliable means to predict clinical outcome, and cytogenetic information is scanty. METHODS: The clinicopathologic features of two cases of malignant PSTT were analyzed. Cytogenetic analysis was performed by comparative genomic hybridization (CGH) and chromosome in situ hybridization (CISH) using frozen tissue and paraffin embedded sections, respectively. RESULTS: Both patients were 32 years old at time of diagnosis. One patient with PSTT presented with menorrhagia, and the other presented with symptoms of missed abortion. Elevated serum human chorionic gonadotropin (HCG) was detected in both patients. Histologic examination showed the typical features of PSTT with high mitotic count (> 5/10 high-power fields). Ovarian and lung metastasis occurred in both patients. Immunohistochemical staining revealed an equal distribution of HCG and human placental lactogen. Cytogenetic studies by CISH showed that karyotypes of these two malignant PSTTs were diploid. Analysis of the tumor tissue by CGH did not show any changes in DNA copy numbers. CONCLUSIONS: The authors' study indicated that the two metastasizing PSTTs had balanced diploid karyotype. The malignant behavior of PSTTs may be not related to the DNA copy number changes. Such cytogenetic study may be useful in distinguishing metastatic PSTT from choriocarcinoma.