PIWIL4 and seminoma: Based on the data that implicate Piwi in transposon silencing, maintenance of genome integrity and exclusively embryonic and/or stem cells expression, it is surprising that a growing body of studies reveal that Hiwi, the human ortholog of Piwi, is expressed in a diverse group of cancers including: seminomas [11], pancreatic [12] and gastric [13] adenocarcinomas, squamous cell carcinomas [14]; and sarcomas [15].