Abstract Human testicular germ cell tumors (TGCTs) are the most frequent solid cancer in Caucasian males between the ages of 15 and 45 years. In spite of the high success rate of current treatment strategies (surgery, irradiation and chemotherapy), TGCTs are the second leading cause of death in this age group. The initiating event, leading to carcinoma in situ (CIS), occurs during embryonal development, offering a window of opportunity for early detection and intervention, thereby preventing the need for intensive (systemic) treatment. CIS is the malignant counterpart of a primordial germ cell, and can be effectively diagnosed using immunohistochemisty for OCT3/4, NANOG, c-KIT and its ligand (stem cell factor, SCF). In addition, SOX17 and SOX2 are informative for the diagnosis of the invasive components seminoma and embryonal carcinoma. Currently, in a clinical setting, these proteins are detected using predominantly immunohistochemistry, an approach that is labor-intensive and non-quantitative. Here we present data on the detection of these proteins using a novel qPCR-based method, Taqman Protein Expression Assay, which is based on the Proximity Ligation Assay (PLATM) technology. The method was first validated on negative controls and a series of TGCT-derived cell lines with efficient siRNA-induced down-regulation of the targets, an informative system for investigating stem cell regulatory circuits. Subsequently, the assay was further developed to enable analysis of both snap frozen and formalin-fixed paraffin-embedded (FFPE) tissues. The assays were found to be fast (results in less than 1 day), highly reproducible (SD less than 0.2 CTs), sensitive (able to detect target protein from as few as 10-100 cells, depending on the level of expression of the protein under investigation), and quantitative. Taqman Protein Expression Assays therefore allow the systematic analysis of multiple proteins within a single small sample in a high throughput set up, and offer unique opportunities for sensitive, specific and quantitative protein detection in both experimental and clinical studies. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1163.