Investigating the Efficacy and Safety of Neoadjuvant Intravesical Instillation of Mitomycin C in Treating High-risk NMIBC Patients

The goal of this clinical trial is to learn if neoadjuvant intravesical instillation of mitomycin C combined with en-bloc surgery works to treat high-risk non-muscle-invasive bladder cancer (NMIBC) patients. It will also learn about the safety of neoadjuvant intravesical instillation of mitomycin C. The main questions it aims to answer are: Does neoadjuvant intravesical instillation of mitomycin C heighten the 1-year recurrence-free survival (RFS) rate for high-risk non-muscle-invasive bladder cancer (NMIBC) patients? What medical problems do participants have when taking neoadjuvant intravesical instillation of mitomycin C? Researchers will compare neoadjuvant intravesical instillation of mitomycin C to a placebo (normal saline) to see if neoadjuvant intravesical instillation of mitomycin C works to treat high-risk NMIBC. Participants will: Take neoadjuvant intravesical instillation of mitomycin C or a placebo twice，1 day and 4 hours before en-bloc surgery Visit the clinic once every 8 weeks for checkups and tests Keep track of the recurrence and progression of the tumor.