Approximately 450 subjects will be randomized. The primary objective of this study is to evaluate the efficacy of intravesical EN3348 as compared with mitomycin C in the treatment of subjects with recurrent or refractory NMIBC. The secondary objective is to evaluate the safety of EN3348 as compared with mitomycin C in the treatment of subjects with BCG recurrent or refractory NMIBC. This study will consist of 4 phases: Screening, Induction, Maintenance and Follow-Up and will be conducted over 3 years.