The goal of this clinical trial is to compare the efficacy and safety of two Bacillus Calmette-Guérin (BCG) substrains (RIVM and Russian) in the treatment of intermediate- and high-risk non-muscle-invasive bladder cancer (NMIBC) in adult patients.

The main questions it aims to answer are:

• Is there a significant difference in recurrence-free survival (RFS) between the BCG RIVM and BCG Russian substrains?
• Is there a significant difference in progression-free survival (PFS) between the two substrains?
• Are there notable differences in the incidence of treatment-related adverse events between the strains? Researchers will compare patients treated with BCG RIVM to patients treated with BCG Russian to determine whether one substrain offers superior clinical outcomes in terms of recurrence, progression, and adverse events.

Participants will:

Undergo transurethral resection of bladder tumor (TURBT) prior to initiating therapy.

Be randomly assigned to receive either BCG RIVM or BCG Russian intravesical therapy.

Receive an induction course of six weekly instillations of the assigned BCG substrain.

Receive maintenance therapy at regular intervals (3, 6, 12, 18, 24, 30, and 36 months) based on risk classification.

Undergo regular follow-up with cystoscopy and urine cytology to assess recurrence, progression, and adverse events.

Inclusion Criteria:

• age ≥18 years,
• histopathologically confirmed NMIBC (stages Ta, T1, or CIS),
• classification as intermediate, high, or very high risk (who either refused or were not suitable candidates for radical cystectomy),
• no prior BCG therapy,
• no evidence of upper urinary tract carcinoma or distant metastases and
• a minimum follow-up period of 12 months.

Exclusion Criteria:

• patients who did not receive adequate BCG therapy (defined as receiving fewer than 5 of the 6 induction doses or fewer than 2 of the 3 maintenance doses),
• patients with a follow-up period of less than 12 months and
• patients who received multiple BCG strains during the follow-up period.