Dietary Animal Protein Intake and Progression-Free Survival in Urothelial and Renal Cell Carcinomas

Background: Dietary fiber intake has been associated with longer PFS on ICB in observational studies, putatively due to effects of fiber on the gut microbiome. However, associations in observational studies may be due to confounding rather than causal relationships. Dietary animal protein intake impacts health and can be correlated with fiber intake. We investigated whether animal protein intake is associated with ICB outcomes in UC and RCC and whether confounding by animal protein intake might account for associations of fiber intake with ICB outcomes. Methods: We conducted a retrospective analysis of a prospectively collected cohort, wherein baseline dietary data were collected using the Willett Food Frequency Questionnaire from pts with advanced UC or RCC initiating ICB at Memorial Sloan Kettering. Associations of diet with clinical outcomes were assessed using univariable and multivariable Cox proportional hazards regression. Results: From 2/2021-6/2022, 86 pts eligible for this analysis were enrolled (UC n = 38; RCC n = 48; median follow-up 14.6 months). Median animal protein intake was 44 g/day (interquartile range [IQR] 31-54), below the American average of 88 g/day. Median fiber intake was 17.2 g/day (IQR 13-24), similar to the American average of 15 g/day. Intake of animal protein and fiber were correlated (Spearman’s rho 0.46, p < 0.001). There were no statistically significant associations of animal protein intake above vs below the median with PFS in either univariable or multivariable models (Table 1). Dietary fiber intake was associated with longer PFS even after adjusting for animal protein intake and clinical covariables (Table 1). Conclusion: Dietary animal protein intake was not associated with PFS among pts with UC and RCC on ICB. The association of dietary fiber with longer PFS could not be attributed to confounding by animal protein intake. Citation Format: Timothy B. Winslow, Ritesh Kotecha, Neha Ratna, David Gavrilov, Cihan Duzgol, Mahnoor Akhlaq, Min Yuen Teo, Ashley M. Regazzi, Samuel Funt, David H. Aggen, Scot Niglio, Maria Carlo, Daniel Lage, Neil Shah, Aditi Gupta, Darren F. Feldman, Martin H. Voss, Robert J. Motzer, Jonathan E. Rosenberg, Gopa Iyer, Brendan John Guercio. Dietary animal protein intake and progression-free survival (PFS) of patients (pts) with advanced urothelial cancer (UC) and renal cell carcinoma (RCC) on immune checkpoint blockade (ICB) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2862.