3211 - Association of MRI Capsular Involvement and Extraprostatic Extension on Metastasis Free and Overall Survival in Localized Prostate Cancer Treated with Radiation

A. Kumar¹, D. LaBella¹, M. C. Snider¹, S. Acklin¹, R. T. Gupta², J. K. Salama¹, and M. J. Boyer¹; ¹Department of Radiation Oncology, Duke University Medical Center, Durham, NC, ²Duke Cancer Center, Durham, NC

Purpose/Objective(s): Multiparametric magnetic resonance imaging (mpMRI) is not currently included in prostate cancer (PC) staging. The purpose of this study was to test the association between mpMRI detected prostate capsule involvement and extraprostatic extension (EPE) with metastasis free survival (MFS) and overall survival (OS) in patients with localized PC treated with radiation. Materials/

Methods: Patients diagnosed with localized PC between 2000-2021 from the Veterans Affairs Prostate Date Core with an mpMRI prior to definitive radiation were identified. Reports were assessed for minor or significant capsular abutment (defined as greater than or equal to 1.5 cm of capsular contact or radiologist’s mention of long segment abutment), extracapsular extension (ECE), seminal vesicle invasion (SVI), or adjacent organ invasion (OI). mpMRI findings impact on MFS by multivariable Fine-Gray competing-risks regression and OS by Cox regression were assessed.

Results: Overall, 1,547 patients were included. Most pre-treatment mpMRIs (84%) occurred after 2016. 692 (45%) patients were Black. 1,113 (72%) patients had non-palpable disease. Median follow-up was 5 years. The 5-year cumulative incidence of metastasis was 10% (95% confidence interval (CI) 8-12%) and death was 9% (95% CI 7-11%). There were 390 (25%) patients with minor capsular abutment, 134 (9%) with significant capsular abutment, 129 (8%) with ECE, 56 (4%) with SVI, and 17 (1%) with OI. After controlling for age, race, prostate specific antigen, grade group, and comorbidities, the presence of significant capsular abutment, ECE, SVI, and OI were independently associated with MFS, but minor capsular abutment was not. On multivariable analysis controlling for the same factors, EPE (ECE, SVI, or OI) was associated with worse OS.

Conclusion: In a modern, real-world cohort of localized PC patients treated with radiation from the largest integrated health system in the United States, significant capsule abutment and EPE on mpMRI are independently prognostic of MFS, but minor capsular abutment is not. EPE is associated with inferior OS. mpMRI should be widely available for patients with PC as it adds prognostic information. Studies are ongoing to define its role as a standard staging tool.

Abstract 3211 – Table 1

MRI Finding	Hazard Ratios (95% Confidence Intervals)
	MFS	OS
No capsule abutment	Reference	Reference
Minor capsule abutment	0.66 (0.40-1.09)
Significant capsule abutment	1.67 (1.05-2.75)	0.98 (0.55-1.78)
Extracapsular Extension	1.86 (1.13-3.08)	1.65 (1.09-2.51)
Seminal Vesicle Invasion	3.13 (1.96-5.99)
Organ Invasion	7.95 (4.03-16)