Prognostic Significance of RB1 Alterations on Outcomes in Metastatic Prostate Cancer.

Purpose: Emerging evidence suggests that RB1 inactivation may be a strong predictor of poor survival for men with prostate cancer (PC); however, large-scale validation is lacking.

Methods: We analyzed whether RB1 alterations are associated with inferior survival in advanced PC and evaluated the impact of co-occurring genomic alterations on outcomes using retrospective data from the Veteran's Health Administration and Veterans Affairs Multi-Omics Analysis Platform for Prostate Cancer from 2016 to 2023.

Results: The primary outcome was overall survival (OS) from onset of metastatic castration-resistant prostate cancer (mCRPC), as well as OS from initiation of life-prolonging therapy other than androgen deprivation therapy, and time to development of mCRPC. Eighty-seven (3.5%) of the 2,512 included patients had an RB1 alteration detected. The median age at diagnosis in the RB1-altered group was 71 (IQR, 65-76) years, and 68 (IQR, 62-73) years in the RB1 wild-type group. The median overall survival from diagnosis of mCRPC was 1.31 years (95% CI, 0.89 to 1.84) in those with an RB1 alteration compared with 2.99 years (95% CI, 2.79 to 3.23). RB1 alteration alone conferred similar poor prognosis when compared with patients who had combined PTEN and TP53 alterations. A dose effect was seen with increasing numbers of tumor suppressor genes (TSGs-RB1, TP53, and PTEN) conferring poorer outcomes. The median survival of patients from diagnosis of mCRPC with zero, one, two, and three TSGs was 3.74, 2.61, 1.61, and 0.87 years, respectively. BRCA2 alterations were not associated with significantly worse outcomes unless accompanied by RB1 alteration.

Conclusion: In this large, real-world cohort of men with mCRPC, RB1 alterations emerged as a strong indicator of poor prognosis and can be used to stratify studies alone or in conjunction with other TSG alterations.