Intravesical GEM/DOCE for HR BCG-Unresponsive NMIBC

The goal of this clinical trial is to learn whether a combination of two chemotherapy drugs, Gemcitabine and Docetaxel, can treat high-grade non-muscle-invasive bladder cancer (HG-NMIBC) in adults whose cancer failed conventional BCG therapy. The drugs are given directly into the bladder (intravesically), one immediately after the other. The study will also assess the safety of this treatment. The main questions it aims to answer are: Can this drug combination effectively treat HG-NMIBC that did not respond to BCG and help prevent the cancer from coming back, offering long-term protection? What side effects or medical issues do participants experience during treatment? Researchers will evaluate this non-surgical approach as a potential alternative to bladder removal surgery (radical cystectomy), with the goal of validating it as a bladder-sparing option in this setting. Participants will: * Go through a screening process, including tumor removal and imaging tests * Receive weekly bladder treatments with Gemcitabine followed by Docetaxel for 6 weeks * If the cancer responds, continue with similar once monthly treatments (maintenance therapy) for up to 2 years * Attend regular check-ups, including bladder exams, urine tests, biopsies, and optional quality-of-life surveys * Possibly receive a second 6-week treatment cycle if the cancer returns early * Be followed for up to 5 years to monitor long-term outcomes