Bacillus Calmette-Guérin (BCG) and Gemcitabine in People With High-Grade Non-Muscle Invasive Bladder Cancer That Came Back After BCG Treatment

Inclusion Criteria: * Recurrent for persistent high-grade NMIBC Ta/T1/Tis (Ta/T1 with CIS is preferred, but not required) within 24 months of the last treatment with BCG (with or without IFN) o Up to 26 months from the last BCG treatment is allowed for the treating physician to perform a transurethral resection of bladder tumor (TURBT) so long as there is evidence of recurrent disease (by positive cytology, imaging, or office cystoscopy) within 24 months of last BCG transurethral resection of bladder tumor (TURBT) * Pathologic confirmation of stage, grade, and urothelial histology by the Department of Pathology at MSK * All visible papillary lesions macroscopically resected within 60 days of treatment initiation * Absence of urothelial carcinoma involving the upper urinary tract (documented by radiological imaging or ureteroscopy) within 12 months from the start of treatment * Receipt of restaging transurethral resection (TUR) for any tumor with invasion into the lamina propria (HGT1) as part of standard care * Age ≥18 years * Karnofsky performance status ≥60% * Informed consent Exclusion Criteria: * Positive pregnancy test * Known contraindications to BCG * History of systemic hypersensitivity reaction or history of febrile systemic BCG reaction * Febrile illness or persistent gross hematuria * Active tuberculosis * Immunosuppression due to congenital or acquired immune deficiency, concurrent immune suppressive disease, systemic cancer therapy, or chronic immunosuppressive therapy other than topical or inhaled corticosteroids * History of or currently being treated for muscle-invasive (i.e., stage T2 or higher) or metastatic urothelial cell carcinoma * Evidence of concurrent extravesical (i.e., urethra, ureter, or renal pelvis) urothelial cell carcinoma * BCG-unresponsive NMIBC as defined by the FDA: * HGT1 within 3 months after an induction BCG course (received ≥5 of 6 doses) * Persistent or recurrent high-grade NMIBC (Tis, Ta, T1) within 6 months of ≥5 of 6 doses of induction BCG therapy and ≥2 of 3 doses of maintenance BCG therapy