A Study of Intravesical Enfortumab Vedotin For Treatment of Patients With Non-muscle Invasive Bladder Cancer (NMIBC)

Inclusion Criteria: * Histologically confirmed, non-muscle invasive urothelial carcinoma with carcinoma in situ (CIS) (with or without papillary disease) * Predominant histologic component (\>50 percent) must be urothelial (transitional cell) carcinoma * Participants must have high-risk Bacillus Calmette-Guerin (BCG) - unresponsive disease, defined as (where adequate BCG therapy is defined as one of the following: 5 of 6 doses of an initial induction course + at least 2 of 3 doses maintenance therapy or 5 of 6 doses of an initial induction course + at least 2 of 6 doses of a second induction course): * Persistent or recurrent CIS alone or with recurrent Ta/T1 (noninvasive papillary disease/tumor invades the subepithelial connective tissue) disease within 12 months of completion of adequate BCG therapy. * Recurrent high-grade Ta/T1 disease within 6 months of completion of adequate BCG therapy, or * T1 high-grade disease at the first evaluation following an induction BCG course (at least 5 or 6 doses) * Participant must be ineligible for or refusing a radical cystectomy * All visible papillary Ta/T1 tumors must be completely resected within 60 days prior to enrollment. * Eastern Cooperative Oncology Group Performance Status score of 0, 1, or 2. Exclusion Criteria: * Current or prior history of muscle-invasive urothelial carcinoma or metastatic disease. * Nodal or metastatic disease as noted on computed tomography (CT) or magnetic resonance imaging (MRI) within 3 months prior to study treatment * Concomitant upper tract urothelial carcinoma as noted on CT or MRI urogram performed within 3 months prior to study treatment * Prior or concomitant urothelial carcinoma of the prostatic urethra within 6 months prior to study treatment * Participants with tumor-related hydronephrosis * Participant has received other systemic anticancer therapy including chemotherapy, biologic therapy, immunotherapy, targeted therapy, endocrine therapy, and/or investigational agent within 4 weeks or intravesical therapy within 6 weeks of first dose of study treatment * Participant has had any prior radiation to the bladder for urothelial cancer