Urinary Microbiota Composition in Treatment-Naïve Bladder Cancer: A Case–Control Study with Tumor Invasiveness Stratification

<i>Background and Objectives</i>: Emerging evidence suggests that the genitourinary microbiota may influence the development and progression of urological malignancies, including bladder cancer. This study aimed to characterize the urinary microbiota at diagnosis in patients with bladder cancer and compare findings with healthy controls. <i>Materials and Methods:</i> Urine samples were collected from 30 patients with treatment-naïve bladder cancer and 20 age- and sex-matched healthy individuals. Microbiota composition was analyzed using 16S rRNA sequencing, and subgroup comparisons were made between muscle-invasive bladder cancer (MIBC) and non-muscle-invasive bladder cancer (NMIBC). Differentially abundant taxa were identified using linear discriminant analysis effect size (LEfSe) with an LDA threshold > 2 and <i>p</i> < 0.05. <i>Results:</i> No significant differences were observed in alpha or beta diversity between patients and controls or between MIBC and NMIBC. At the phylum level, <i>Firmicutes</i> was dominant in both groups but relatively more abundant in bladder cancer cases. <i>Enterococcus</i> was the most abundant genus in the cancer group (35.0%) and especially in MIBC (58.0%), while <i>Lactobacillus</i> was more prevalent in healthy controls (19.8% vs. 9.5%). At the species level, <i>Veillonella dispar</i> was notably enriched in MIBC cases (70.9%) compared to NMIBC (3.9%). LEfSe analysis revealed significant enrichment of <i>Ralstonia</i>, <i>Microbacterium</i>, and <i>Facklamia</i> in patients with bladder cancer, while <i>Parvimonas</i>, <i>Sneathia</i>, <i>Gemella</i>, and <i>Acinetobacter guillouiae</i> were more abundant in controls. <i>Conclusions:</i> These findings highlight preliminary microbiota differences associated with bladder cancer and tumor invasiveness; however, the results are exploratory and larger studies are required to evaluate their diagnostic or clinical relevance.