Abstract 162: Cholesterol metabolism gene expression and prostate cancer-specific outcomes in radiotherapy-treated patients

Introduction Dysregulated lipid metabolism is a hallmark of prostate cancer. Furthermore, use of the cholesterol lowering statin drugs has been linked to a reduced risk of lethal prostate cancer. To understand the molecular pathways implicated in this relationship, we examined the association between differential expression of genes involved in intratumoral cholesterol metabolism in prostate tumor biopsies and prostate cancer-specific outcomes. Methods Tumor biopsy gene expression data from 242 men diagnosed with localized/locally advanced prostate cancer and treated with radiotherapy and androgen deprivation therapy was analyzed. A total of 71 genes involved in cholesterol transport, biosynthesis and regulation were selected from the Reactome pathway database, with additional genes involved in cholesterol metabolism extracted from literature. For each gene, expression levels were dichotomized by median expression level. Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for associations of gene expression with biochemical recurrence and metastasis. Models were adjusted for age at diagnosis and Gleason score. Multiple-testing correction was performed using the Bonferroni correction method. Results During a median follow-up of 10.4 years, 72 (30%) patients experienced biochemical recurrence and 32 (13%) developed metastatic disease. Differential expression of several genes was found to be associated with risk of biochemical recurrence and metastasis, though none remained statistically significant following Bonferroni correction. However, several genes showed similar patterns of association with risk of biochemical recurrence and of metastasis, an association which remained similar following adjustment for age and Gleason score. Low (below median) expression of FDFT1, a gene encoding squalene synthase, a key enzyme in cholesterol biosynthesis, was associated with an increased risk of biochemical recurrence (HR 1.87; 95% CI, 1.15-3.01) and metastasis (HR 3.52; 95% CI, 1.52-8.16). High (above median) expression of SLCO1B3, a gene encoding an organic anion transporting polypeptide transporting a variety of small molecules including statins, was associated with higher risk of biochemical recurrence (HR 2.14; 95% CI, 1.31-3.49) and metastasis (HR 2.70; 95% CI, 1.25-5.90). Conclusion These hypothesis-generating results point to a potential role for altered intratumoral cholesterol metabolism in prostate cancer-specific outcomes. Our findings highlighting differential expression of FDFT1 and SLCO1B3, genes involved in cholesterol biosynthesis and anion transport, respectively, in association with risk of biochemical recurrence and metastasis may provide clues as to the mechanistic pathways of most importance. Validation in other prostate cancer gene expression datasets is required. Citation Format: Sarah J. Winter, Sophia Halliday, Konrad H. Stopsack, Sarah O. Osman, Alan R. Hounsell, Gillian Prue, Suneil Jain, Emma H. Allott. Cholesterol metabolism gene expression and prostate cancer-specific outcomes in radiotherapy-treated patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 162.