Expression of the axon guidance protein Robo1 in pancreatic ductal adenocarcinoma from smokers compared to nonsmokers.

Abstract

305 Background: The most important modifiable risk factor for the development of pancreas cancer is smoking, which accounts for up to 25% of pancreatic ductal adenocarcinomas (PDAC; Maisonneuve P, Lowenfels AB: Epidemiology of pancreatic cancer: an update. Digestive Diseases 28:645-656, 2010), and the incidence of PDAC correlates with smoking prevalence (Weiss W, Benarde MA: The temporal relation between cigarette smoking and pancreatic cancer. American journal of public health 73:1403-1404, 1983). A recently published Ingenuity Pathway Analysis of GWAS genotype and risk factor data from the Pancreatic Cancer Case Control Consortium demonstrated that axon guidance signalling genes were significantly overrepresented in smokers (Tang H, Wei P, Duell EJ, et al: Axonal guidance signaling pathway interacting with smoking in modifying the risk of pancreatic cancer: A gene and pathway-based interaction analysis of GWAS data. Carcinogenesis:bgu010, 2014) and we aimed to investigate this link in our cohort. Methods: Tissue from resected PDAC were obtained from 200 patients via the Australian Pancreatic Cancer Genome Initiative with patient consent and ethical approval. Immunohistochemistry was performed on TMAs with the anti-Robo1 antibody (ab7279). The sections were scored on a 4-point scale of 0, 1, 2 and 3 intensity. All sections were scored blindly by two independent reviewers. Results: Robo1 protein expression is found in the normal pancreas, predominantly in acinar cells. In PDAC, Robo1 expression is predominantly in epithelial ductal cells. Most PDACs have Robo1 expression with an overall mean score of 1.65±0.05. 20 out of 200 patients were current smokers at the time of their pancreatectomy, 97 were never smokers, the remainder were ex-smokers. The mean score for smokers was 2.1± 0.1 and for never smokers 1.6±0.1 (p = 0.0003). Genomic analysis did not demonstrate any mutations in the Robo1 gene. There were 7 cases of loss of heterozygosity for Robo1; none of these were current smokers and they had an average score of 1.25±0.17. Conclusions: In addition to our genomic (Biankin AV, Waddell N, Kassahn KS, et al: Pancreatic cancer genomes reveal aberrations in axon guidance pathway genes. Nature 491:399-405, 2012) and methylation data (Nones K, Waddell N, Song S, et al: Genome‐wide DNA methylation patterns in pancreatic ductal adenocarcinoma reveal epigenetic deregulation of SLIT‐ROBO, ITGA2 and MET signaling. International Journal of Cancer, 2014), we provide the results of protein expression of Robo1 in a clinically annotated cohort of 200 cases of PDAC. We demonstrate that patients who are currently smoking have enhanced Robo1 expression. Preliminary results indicate that this may confer a poorer prognosis when coupled with high SLIT2 expression.