3225 - Exploring Gene Expression and Pathway Analysis in Localized Prostate Cancer: Insights from a Retrospective Cohort Study with a Focus on Hypoxia and Angiogenic Biomarkers Post-EBRT and HDR-BTb

T. Lodhi^1,2, M. Reardon², A. M. Rojas³, A. Choudhury^1,2, and P. Hoskin^2,4; ¹Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom, ²Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom, ³Mount Vernon Cancer Centre, London, United Kingdom, ⁴Mount Vernon Cancer Centre, Middlesex, United Kingdom

Purpose/Objective(s): Prostate cancer (PCa) remains the most prevalent male cancer worldwide. Despite a phase-III trial demonstrating improved relapse-free survival (RFS) in localised PCa with the addition of high-dose-rate brachytherapy boost (HDRBTb) to external beam radiotherapy (EBRT), ~21% of patients still experience relapse (Hoskin 2021). Immunohistochemistry has demonstrated the prognostic significance of hypoxia and angiogenic biomarkers in patients undergoing EBRT +/- HDRBTb (Bhattacharya 2019). However, genomic biomarkers have not been investigated. We hypothesise that hypoxia and angiogenesis gene expression is associated with post-radiotherapy outcomes and will stratify for HDRBTb dose escalation. Materials/

Methods: Prostate biopsy samples from a phase 3 randomised controlled trial comparing EBRT alone versus EBRT combined with HDR-BTb (trial number: ISRCTN98241100) were analysed using Clariom S microarrays to obtain whole transcriptomes. The primary endpoint was biochemical relapse-free survival (bRFS) using the Phoenix definition (2ng/mL above nadir), with distant metastasis-free survival (MFS) and overall survival (OS) as secondary endpoints. Survival was analysed with respect to gene expression levels of hypoxia-inducible factor 1 alpha (HIF1a), glucose transporter 1 (GLUT1), osteopontin (OPN), CD34, and a 28-gene hypoxia signature (Yang 2019) using Kaplan-Meier and multivariate Cox proportional hazards model. All analyses were conducted using R software (R Core Team, 2023).

Results: 61 men were available for analysis, with a median follow-up of 131 months. Using Kaplan Meier analysis, low HIF1a was linked with improved MFS (p=0.02) and OS (p=0.01) but not bRFS. Meanwhile, GLUT1, CD34, OPN and the 28-gene hypoxia signature expression levels showed no significant influence on bRFS, MFS, or OS. HDRBTb significantly improved bRFS in Kaplan Meier (p<0.01) and multivariate analysis (HR 0.55 [95%CI 0.3-0.97], p=0.04) but not MFS or OS. In Kaplan Meier analysis, low levels of GLUT1 (p=0.01) and HIF1a (p<0.01) indicated a significant bRFS benefit from HDRBTb. No difference in bRFS, MFS and OS was evident in multivariate Cox analysis by gene expression (Table 1).

Conclusion: In this small study, angiogenesis and hypoxia biomarkers are not associated with the benefit of dose escalation from HDRBTb. Larger cohorts and prospective studies are required for further investigation.

Abstract 3225 – Table 1: Multivariate analysis by treatment or gene expression (N=61).

Variable	BRFS		MFS		OS
	HR (95% CI)	P value	HR (95% CI)	P value	HR (95% CI)	P value
EBRT & HDRBTb vs EBRT	0.55 (0.3- 0.97)	0.0406	1.28 (0.44- 3.13)	0.63	1.08 (0.56- 2.13)	0.81
GLUT1	1.18 (0.75- 1.89)	0.47	1.30 (0.58- 2.97)	0.52	1.25 (0.71- 2.18)	0.44
OPN	1.11 (0.89- 1.38)	0.33	0.99 (0.67- 1.49)	0.98	1.12 (0.92- 1.45)	0.19
CD34	1.16 (0.71- 1.89)	0.55	1.57 (0.66- 3.7)	0.31	0.92 (0.52- 1.64)	0.78
HIF1a	0.83 (0.60- 1.13)	0.23	1.03 (0.65- 1.65)	0.89	0.92 (0.53- 1.61)	0.67
Hypoxia Score	0.81 (0.57- 1.17)	0.26	0.81 (0.65- 1.65)	0.47	1.17 (0.81- 1.68)	0.41