BACKGROUND: Bladder cancer is a growing health concern, especially in developing countries like Türkiye. Intravesical Bacillus Calmette-Guérin (BCG) immunotherapy is essential for reducing recurrence and progression in non-muscle invasive bladder cancer (NMIBC). However, it can cause local and systemic adverse effects linked to bacterial virulence, allergic reactions, or nosocomial infections. Data from randomized studies on BCG side effects are limited, with severe cases often reported in case studies. This study investigates the association between intravesical BCG immunotherapy and its adverse effects. METHODS: A retrospective analysis was conducted on 239 patients who underwent BCG immunotherapy between 2017 and 2024. Detailed demographic, clinical, and laboratory data were collected, and the adverse effects that developed following BCG therapy were evaluated. Descriptive statistics, including medians, counts, and percentage distributions, were calculated, and logistic regression analysis was performed to identify factors influencing the development of adverse effects. RESULTS: Adverse effects related to BCG immunotherapy were observed in 63.1% of the patients. The most common minor adverse effects were hematuria, dysuria, and cystitis, while major adverse effects included sepsis and lymphadenopathy. The analyses revealed that elevated aspartate aminotransferase (AST) levels and the presence of CONCLUSION: BCG immunotherapy is an effective treatment method for NMIBC
however, the adverse effects that occur during treatment must be closely monitored. Elevated AST levels, the presence of specific pathogens in urine cultures, and the number of BCG doses administered are significant factors that increase the risk of adverse effects. These findings highlight the necessity for more careful monitoring throughout the treatment process.