RITE-EUROPE (Radiofrequency-Induced Thermochemotherapy Effect-EUROPE)

Inclusion Criteria: 1. Patients with CIS, with or without coexisting papillary NMIBC, who either: * fail to achieve a disease-free status by 6 months after initial BCG therapy, with maintenance or re-induction at 3 months due to either persistent or rapidly recurrent disease, or * experience a worsening in NMIBC state following initial BCG therapy presenting with a new NMIBC instance, other than TaLG. 2. All clinical, intra-operative and pathological items for the EAU risk stratification must be documented including a bladder map. 3. Patients with papillary disease must have undergone a repeat TUR: * if the initial TUR was incomplete. * if there was no muscle in the specimen after the initial TUR (except in TaLG tumors). * in all T1 tumors. TUR of T1 sites must include muscle. * in all HG tumors \> 3cm. 4. CT-IVU or IVU confirmation of absence of tumor(s) in the upper tract, kidney and ureters performed within 6 months before the treatment initiation in selected cases as recommended in latest EAU guidelines published prior to screening. If IVU protocol not available or contrast allergy/poor renal function preclude such imaging, then non-contrast CT or MRI of the abdomen/pelvis within the same timeframe will suffice. 5. Visual inspection to exclude urothelial carcinoma (UC) in the urethra during cystoscopy. 6. Biopsy of the prostatic urethra in male patients prior to recruitment to exclude UC of the prostatic urethra, in patients with: * tumor of trigone, * tumor of bladder neck, or * abnormal prostatic urethra 7. All patients must have urine cytology collected from either voided urine or bladder wash within the screening period prior to recruitment. 8. All patients must have prostatic urethral biopsies collected within the screening period prior to recruitment. 9. Age ≥ 18 yrs. 10. Normal kidneys and ureters. 11. Pre-treatment hematology and biochemistry values within the limits: * Hemoglobin ≥ 10 g/dl * Platelets ≥ 150 x 10\^9/L * WBC ≥ 3.0 x 10\^9/L * ANC ≥ 1.5 x 10\^9/L * Serum creatinine \< 1.5 x ULN * SGOT \< 1.5 x ULN * SGPT \< 1.5 x ULN * Alkaline phosphatase \< 1.5 x ULN 12. Negative pregnancy test for women of childbearing potential. 13. A life expectancy at least of the duration of the study (up to 13 months). 14. Patients unfit or unwilling to have a full or partial (if appropriate) cystectomy. 15. Signed informed consent. Exclusion Criteria: 1. Non-UC tumor of the urinary tract. 2. Upper tract and intramural tumors (e.g., in ostium). 3. Positive selective cytology from the upper tract. 4. History of stage \> T1 UC. 5. Papillary tumor in repeat TUR in patients diagnosed with HG \> 3cm and/or T1 in the initial TUR. 6. Papillary tumor ≥ T1 in repeat TUR 7. Known or suspected reduced bladder capacity. Patients will have a US estimation of maximum bladder capacity or void spontaneously the maximum they can retain in their bladder, and this will be used to determine urine volume. A minimum volume of 250 ml is required. 8. Bleeding disorder. 9. Macrohematuria of ≥ 250 RBC/uL or equivalent (e.g., \> "+++" erythrocytes in a dipstick analysis) within 4 weeks before treatment start. 10. Lactating women. 11. Women of childbearing potential unwilling or unable to use adequate contraception if sexually active. 12. More than a maintenance dose of oral corticosteroids (maintenance dose is defined as the same dose regimen over the past 6 months for a condition requiring continual corticosteroid treatment) or patients with an immunocompromised state for any reason. 13. More than low-dose methotrexate (\>17.5 mg once a week). 14. Other malignancy within the past 5 years, except: non-melanomatous skin cancer cured by excision, surgically treated carcinoma in situ of the cervix or ductal CIS (DCIS)/lobular CIS (LCIS) of the breast or stable prostate cancer (under active surveillance or hormone control) with a life expectancy of more than 5 years. 15. Any known allergy (e.g., to MMC) or adverse event that would prevent a prospective study participant from receiving the study treatment. 16. Known untreated urethral strictural disease or bladder neck contracture or any other condition that may prevent catheterization with 21F catheter. Patients may undergo dilation or urethral incision before entering the study. 17. Bladder diverticula with cumulative diameter \> 1cm or tumor in a diverticulum. 18. UTI at any time within 4 weeks before treatment start. 19. Significant urinary incontinence (spontaneous, requiring use of pads). 20. History of pelvic irradiation. 21. Patients with implanted electronic devices (such as cardiac pacemakers) unless they receive permission from their treating physician (e.g., cardiologist) and are monitored by a treating physician during the treatment session. 22. Participation in another study, unless discussed with and approved by the study manager.