BCG in Combination With Durvalumab in Adult BCG-naïve, High-risk NMIBC Participants (PATAPSCO)

Inclusion Criteria: BCG-naïve (defined as participants not having received prior intravesical BCG or who previously received but stopped BCG more than 3 years before study entry). Local histological confirmation (based on cytology and/or pathology report) of high-risk transitional cell carcinoma of the urothelium of the urinary bladder confined to the mucosa or submucosa. Complete resection of all Ta/T1 papillary disease prior to enrollment, with the transurethral resection of bladder tumor (TURBT) removing high-risk NMIBC (non-muscle invasive bladder cancer) performed not more than 4 months before enrollment in the study. No prior radiotherapy for bladder cancer. A life expectancy of at least 12 weeks (90 days). Adequate organ and marrow function World Health Organization/Eastern Cooperative Oncology Group performance status of 0 or 1 at screening No prior exposure to immune-mediated therapy of cancer A candidate for BCG treatment. Local histological confirmation (based on cytology and/or pathology report) of high-risk transitional cell carcinoma of the urothelium of the urinary bladder confined to the mucosa or submucosa. A high-risk tumor is defined as one of the following: T1 tumor; High-grade/G3 tumor; CIS. Exclusion Criteria: Evidence of muscle-invasive, locally advanced, metastatic, and/or extra-vesical bladder cancer (ie, T2, T3, T4, and / or Stage IV). Predominantly variant histology such as micropapillary, plasmacytoid, nested, sarcomatoid, microcystic, squamous and adeno variants of UC representing > 50% of tumor tissue or other than urothelial tumors as assessed by pathology. Evidence of lymphovascular invasion of bladder tumor, except if treatment with BCG is deemed to be the only clinically viable treatment. Immediate cystectomy is indicated. Known or documented absolute and/or relative contraindication of adjuvant intravesical BCG treatment. Concurrent extravesical, non-muscle-invasive transitional cell carcinoma of the urothelium. History of allogenic organ transplantation. Participants with any history of allogenic stem cell transplantation are also excluded. Active or prior documented autoimmune or inflammatory disorders. Participants with hypothyroidism stable on hormone replacement. History of active primary immunodeficiency. Active infection including hepatitis B (known positive HBV/HBsAg result), HCV, or HIV 1/2 (positive HIV) antibodies. Current or prior use of immunosuppressive medication within 14 days before the first durvalumab dose. Female participants who are pregnant or breastfeeding or male or female participants of reproductive potential who are not willing to employ highly effective birth control. Any concurrent chemotherapy, study intervention, biologic or hormonal therapy for cancer treatment; uncontrolled intercurrent illness; History of another primary malignancy except for Malignancy treated with curative intent and with no known active disease ≥ 2 years; Adequately treated nonmelanoma skin cancer or lentigo maligna without evidence of disease; Adequately treated CIS without evidence of disease; Prostate cancer of stage ≤ T2cN0M0 without biochemical recurrence or progression that in the opinion of the Investigator does not require active intervention. Previous or concurrent treatment with potent systemic immunostimulatory agents