Abstract 5: Identification of androgen receptor (AR) splice variants, AR somatic mutations and TMPRSS2:ETS fusion genes in prostate cancer FFPET by qRT-PCR.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Prostate Cancer (PCa) is the third most common cause of death from cancer in men of all ages. Surgical or medical castration is one of the most common treatments for patients with advanced PCa; however a majority of patients develop castration resistant prostate cancer (CRPC), tumor relapse, which remains to be the second leading cause of cancer-related deaths of men in the US. Androgen receptor (AR) signaling is shown to play a critical role in the development and progression of PCa. Genetic aberrations within AR, including constitutively active AR splice variants and AR point mutations have been identified in CRPC. The most common AR splice variants lack the ligand-binding domain (LBD), which is often the target of CRPC therapies. Therefore, presence of these variants may act as a mechanism of resistance to AR-targeted therapies leading to the progression of prostate tumor growth. Additional PCa specific genetic aberrations include fusions between the androgen-related gene, TMPRSS2 and the ETS transcription factors, ERG (predominant) and ETV1. These fusion events are frequently associated with more aggressive prostate cancers leading to poorer prognosis. In this study, we developed TaqMan qRT-PCR assays to evaluate the presence of several previously identified AR splice variants, including ARV1, ARV3/V7, ARV567 and ARV8, AR somatic mutations, including L701H, V715M, H874Y and T877A, along with TMPRSS2 fusion genes, TMPRSS2:ERG and TMPRSS2:ETV1, in two independent PCa FFPET sample sets. The first sample set consisted of 42 Prostate adenocarcinomas ranging from stage II to stage IV. Results showed that ARV1 and ARV3/V7 were the most prevalent variants with 92% of all samples showing expression of either or both variant. TMPRSS2: ERG was present in 72% of all samples tested, with a high concordance to AR variant expression, prevalent in later stage (III/IV) PCa samples. The second sample set consisted of 8 prostate adenocarcinomas, including matched adjacent normal FFPET. Similar expression of the AR variants was observed in both the tumor and matched normal samples, however tumor prostate samples showed a higher and more prevalent expression (66.67%) of the TMPRSS2: ERG fusion gene than in the matched normal samples (33%). None of the four AR mutations evaluated were detected in either sample set. Overall, these findings demonstrate a strong presence of both AR splice variants and the TMPRSS2: ERG fusion gene in the prostate cancer patient population, supporting evidence for a functional role of these markers in PCa diagnosis and disease progression. Furthermore, presence of LBD negative AR splice variants indicates an attractive biomarker for stratification of the patient population resistant to AR targeted therapies. Citation Format: Dana S. Gaffney, Gabriela Martinez, Katherine Bell, Suso Platero, Deborah Ricci, Jayaprakash Karkera. Identification of androgen receptor (AR) splice variants, AR somatic mutations and TMPRSS2:ETS fusion genes in prostate cancer FFPET by qRT-PCR. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5. doi:10.1158/1538-7445.AM2013-5