BLOSSOM Dietary Habits and 1-Year Intravesical Recurrence in High-Risk Non-Muscle-Invasive Bladder Cancer Treated with BCG

Evidence on modifiable post-diagnosis factors influencing outcomes after intravesical Bacillus Calmette–Guérin (BCG) therapy for high-risk non-muscle-invasive bladder cancer (NMIBC) is limited. In this exploratory, feasibility-focused prospective multicenter cohort (March 2023–November 2024), BCG-naïve patients completed repeated interviewer-administered 24 h dietary recalls; prespecified food groups, selected foods, and nutrients were screened for associations with 1-year intravesical recurrence using Firth’s penalized logistic regression adjusted a priori for age, sex, and total energy intake, with false discovery rate control within each exposure family. Forty-six patients were enrolled; 41 had evaluable recurrence status, including 8 recurrences (19.5%). Participants were predominantly overweight (mean body mass index (BMI) 28.4 kg/m2) and had low adherence to a Mediterranean dietary pattern (median Mediterranean Adequacy Index 2.25). No dietary exposure met the within-family false discovery rate threshold; the smallest q-value was 0.361. Nominal inverse associations were observed for leafy green vegetables (OR per 1 SD 0.385; 95% CI 0.101–0.972) and for energy-adjusted zinc (OR 0.280; 95% CI 0.069–0.802) and magnesium intakes (OR 0.260; 95% CI 0.045–0.872), but these did not remain significant after FDR adjustment. These exploratory signals warrant replication in larger, biomarker-informed cohorts incorporating dietary biomarkers and immune profiling during BCG. Given the limited sample size and low number of recurrence events, these findings are strictly hypothesis-generating and should not be interpreted as evidence of definitive protective or risk dietary factors.