Genes involved in tumorigenesis may be targets for cancer immunotherapy. For many tumor types, molecular signatures do not yet exist. Methods that identify novel, tissue-specific tumor-related genes therefore have potentially important implications for developing cancer immunotherapy. Here, we used cross-reactive serological analysis of recombinant cDNA expression (CR-SEREX) to identify the novel testicular cancer-related gene, rat testicular antigenic protein 2 (RTAP2). We identified two RTAP2 splice variants (RTAP2a and RTAP2b) encoding 191 and 358 amino acid proteins, respectively. RTAP2a and RTAP2b proteins have identical N-termini but different C-terminal regions arising from alternative splicing of exon 4. Bioinformatics and reverse transcription-polymerase chain reaction (RT-PCR) revealed that the RTAP2a transcript was expressed selectively in adult testis and several tumor cell lines, while RTAP2b was ubiquitous. Our results suggest that RTAP2a may contribute to testicular development and tumorigenesis, and may be a candidate gene for cancer immunotherapy.