Predictors of BCG Therapy Complications inNon-Muscle-Invasive Bladder Cancer: AClavien-Dindo-Based Study

<p style="text-align:justify;"> Background: Intravesical Bacillus Calmette-Guérin (BCG) therapy is the standard adjuvant treatment for non–muscle-invasive bladder cancer (NMIBC), particularly in patients with carcinoma in situ, following transurethral tumor resection. Despite its proven oncological benefits, BCG therapy may be associated with a wide range of local and systemic adverse events. This study aimed to evaluate the clinical significance of BCG-related complications across the full severity spectrum and to assess their impact on treatment continuation using the Clavien–Dindo classification system. <p style="text-align:justify;"> Methods: This retrospective study included 694 patients with bladder cancer who received intravesical BCG therapy between 2004 and 2024. Ethical approval was obtained prior to data collection. Patient demographics, comorbidities, tumor characteristics, and treatment details were recorded. Freeze-dried BCG (12.5 mg) was administered intravesically according to induction and maintenance protocols. Adverse events occurring during therapy were systematically classified using the Clavien–Dindo system. The primary outcome was the occurrence of any BCG-related complication. The median follow-up duration was 34 months. <p style="text-align:justify;"> Results: The study cohort comprised 580 men (83.6%) and 114 women (16.4%), with a mean age of 65.1 ± 7.5. Maintenance BCG therapy was administered to 295 patients (42.5%). A total of 122 patients (17.6%) experienced BCG-related complications, the majority of which were low-grade (Clavien–Dindo grade ≤2). Severe complications were rare. In multivariate logistic regression analysis, increasing age (odds ratio [OR]: 1.055; 95% confidence interval [CI]: 1.033–1.078; p < 0.001) and high tumor grade (OR: 2.473; 95% CI: 1.379–4.436; p = 0.002) were identified as independent predictors of complications. <p style="text-align:justify;"> Conclusions: Intravesical BCG therapy is generally safe and well tolerated. However, advanced age and high tumor grade are associated with an increased risk of treatment-related adverse events. These findings highlight the importance of careful patient selection, close monitoring, and individualized management strategies, particularly in elderly patients undergoing BCG therapy.