Allelic loss of the PTEN gene and mutation of the TP53 gene in choriocarcinoma arising from gastric adenocarcinoma: analysis of loss of heterozygosity in two male patients with extragonadal choriocarcinoma

A tumor suppressor gene at 10q23.3, designated PTEN, encoding a dual-specificity phosphatase with lipid and protein phosphatase activity, has been shown to play an essential role in the pathogenesis of a variety of human cancers. Frequent mutations and deletions of PTEN genes are found in cancer. Little is known, however, about the role that PTEN plays in the pathogenesis of a primary choriocarcinoma derived from gastric adenocarcinoma, an extremely rare choriocarcinoma, or in extragonadal retroperitoneal choriocarcinoma. In this study, genetic alterations occurring in extragonadal choriocarcinoma in two Japanese male patients were examined. Loss of heterozygosity (LOH) analysis using a polymorphic marker of the PTEN gene, IVS4 + 109ins/delTCTTA, revealed a hemizygous deletion of PTEN not only in the primary gastric choriocarcinoma, but also in the gastric adenocarcinoma. Microsatellite marker D12S1051 likewise showed LOH in both the primary gastric choriocarcinoma and the gastric adenocarcinoma. Mutational analysis of the TP53 gene revealed a point mutation in exon 5 (A536G), which resulted in H179R in the gastric choriocarcinoma but not in the gastric adenocarcinoma. No LOH was found for PTEN in an extragonadal retroperitoneal choriocarcinoma. Microsatellite marker D9S162 showed LOH in the extragonadal retroperitoneal choriocarcinoma, but not in the primary gastric choriocarcinoma. These results indicate that LOH of the PTEN gene and of D12S1051 is the molecular pathogenesis of the gastric adenocarcinoma, and the mutation of the TP53 gene is an additional hit for the oncogenesis of choriocarcinoma arising from gastric adenocarcinoma. However, LOH of the PTEN gene is not a common molecular event for pathogenesis of extragonadal choriocarcinoma. In addition, it was found that expression of PTEN is significantly decreased in the nuclei of syncytiotrophoblast-like cancer cells, compared with those of cytotrophoblast-like cancer cells in choriocarcinoma.