Background: Most patients would defer using androgen deprivation therapy (ADT) with radiation therapy (RT) when the number-needed-to-treat (NNT) exceeds 25 persons to prevent 1 from developing metastasis, corresponding to an absolute benefit of 4%.¹ However, no tools for estimating personalized NNT or absolute benefit from ADT exist. We aimed to quantify personalized absolute benefit and NNT for persons receiving ADT added to single modality RT. Methods: The clinical cell-cycle risk (CCR) score combines the University of California, San Francisco’s Cancer of the Prostate Risk Assessment and the cell cycle progression molecular score to accurately assess prostate cancer aggressiveness. The effect of ADT added to RT was modeled using a 10-year risk of metastasis as a function of continuous CCR score for patients treated with RT alone. The relative benefit of ADT added to RT to reduce distant metastasis was modeled using published data from The Meta-Analysis of Randomized trials in Cancer of the Prostate (MARCAP) which utilized several prospectively randomized RT±ADT trials.² The average absolute benefit was calculated for patients with CCR scores above and below a prespecified multimodality treatment threshold (MTT) using the distribution of scores in a cohort of patients commercially tested by Myriad Genetics. Results: The commercially tested cohort consisted of 56,485 patients spanning all National Comprehensive Cancer Network risk categories (33.7% very low/low risk, 29.8% favorable intermediate risk, 25.6% unfavorable intermediate risk, 11.0% high/very high risk), with 87.2% having CCR scores at or below the MTT and 12.7% with CCR scores above the threshold. The average absolute benefit of ADT treatment was 0.86% (NNT=116) for patients with CCR scores below the MTT and 8.2% (NNT=12) for patients with CCR scores above the MTT. Patients with CCR scores at precisely the MTT had a predicted absolute benefit of 3.7% (NNT=27). Conclusions: The Prolaris test can accurately predict an individual's benefit of adding ADT to RT, and the risk threshold is consistent with patient attitudes about when to use or omit ADT. 1. Spratt DE, Tward JD: IJROBP 108:899-902, 2020. 2. Kishan AU, Sun Y, Hartman H, et al. Lancet Oncol 23:304-316, 2022.