Carcinoma In Situ (CIS): Is There a Difference in Efficacy between Various BCG Strains? A Comprehensive Review of the Literature

Simple Summary Carcinoma in situ of the bladder is an aggressive type of non-muscle invasive bladder cancer characterized as a flat, high-grade tumour confined to the urothelial layer. Non-muscle invasive bladder cancer comprises approximately 75% to 80% of all bladder cancers, with Carcinoma in situ found in about 10% of cases. Intravesical instillations of Bacillus Calmette-Guérin immunotherapy is the standard of care for high-risk and intermediate-risk papillary non-muscle invasive bladder cancer as well as for Carcinoma in situ. Evidence supports that the different Bacillus Calmette-Guérin strains, despite genetic variability, are equally effective clinically for preventing the recurrence and progression of papillary non-muscle invasive bladder cancer. The available evidence regarding possible differences in clinical efficacy between various Bacillus Calmette-Guérin strains specifically against Carcinoma in situ is lacking. We therefore reviewed the literature on this topic. We found that the clinical efficacy of the various Bacillus Calmette-Guérin strains against Carcinoma in situ appears similar. However, our conclusions should be considered with caution as most studies were underpowered, and none of the trials were designed as head-to-head comparisons. Randomized studies should be encouraged in this space to draw definitive conclusions. Abstract Introduction: Intravesical Bacillus Calmette-Guérin (BCG) immunotherapy is the standard of care for high-risk and intermediate-risk non-muscle-invasive bladder cancer (NMIBC) as well as for Carcinoma in situ (CIS). Evidence supports that the different BCG strains, despite genetic variability, are equally effective clinically for preventing the recurrence and progression of papillary NMIBC. The available evidence regarding possible differences in clinical efficacy between various BCG strains in CIS is lacking. Methods: We reviewed the literature on the efficacy of different BCG strains in patients with CIS (whether primary, secondary, concomitant, or unifocal/multifocal), including randomized clinical trials (RCTs), phase II/prospective trials, and retrospective studies with complete response rates (CRR), recurrence-free survival (RFS), or progression-free survival (PFS) as endpoints. Results: In most studies, being RCTs, phase II prospective trials, or retrospective studies, genetic differences between BCG strains did not translate into meaningful differences in clinical efficacy against CIS, regardless of the CIS subset (primary, secondary, or concurrent) or CIS focality (unifocal or multifocal). CRR, RFS, and PFS were not statistically different between various BCG strains. None of these trials were designed as head-to-head comparisons between BCG strains focusing specifically on CIS. Limitations include the small sample size of many studies and most comparisons between strains being indirect rather than head-to-head. Conclusions: This review suggests that the clinical efficacy of the various BCG strains appears similar, irrespective of CIS characteristics. However, based on the weak level of evidence available and underpowered studies, randomized studies in this space should be encouraged as no definitive conclusion can be drawn at this stage.