The investigartors will conduct a randomized, multinational study with the aim to assess if the efficacy of a dose dense chemoablation with Mitomycin C (MMC) with adjuvant BCG in non-responding patients is superior regarding long term effect compared to standard treatment with trans urethral resection of bladder tumors (TURBT) and adjuvant intravesical instillation therapy in patients with recurrent Ta LG tumors.

The study is a natural follow-up study following the pivotal NICSA trial supported by the Danish Cancer Society that has lead to the initial change in the European guidelines. In order to not only be comparable to current standard, but also to improve clinical outcome and furthermore confirm the previous findings, the investigators here suggest to implement at patient tailored approach through a new multicenter RCT.

The investigators hypothesize that chemoablation with MMC in patients with recurrent Ta LG tumors will result in a permanent low recurrence rate in patients with complete response, whereas patients without complete response can be selected for adjuvant BCG which theoretically is more efficient in this select patient group. This will potentially result in a more favorable long term recurrence free survival (RFS) rate compared to the current standard regimen where all patients are treated with TURBT and adjuvant instillation therapy.

The incidence of bladder cancer in Denmark is almost 2,000 per year. Of these, 75% have non-muscle invasive bladder cancer (NMIBC). The yearly recurrence rate of NMIBC is approximately 35% and the disease is therefore one of the most costly cancers to manage on a per patient basis, due to the cost of operative procedures, follow-up cystoscopies and instillation therapies

Inclusion Criteria:

• Tumour recurrence after previous urothelial tumour of Ta low-grade
• Tumours smaller than 2 cm in diameter
• Negative urine cytology (optional)
• ≥18 years of age
• Ability to understand and comprehend the provided written and oral information
• Has provided written consent

Exclusion Criteria:

• Known history of invasive tumour of the bladder (T1+)
• Known history of CIS of the bladder
• Previous MMC or BCG-treatment except for single instillations following previous TURBTs
• Known allergy or intolerance to MMC
• Solid tumour with suspicions of invasion
• Tumour in the bladder neck or urethra
• Suspicion of CIS (positive cytology with high-grade neoplastic cells combined with suspicious flat lesions seen at cystoscopy)
• Small bladder volume (less than 100 ml) or incontinence
• Prior radiation therapy to the pelvic area, as radiation affects the bladder function and instillation therapy is a suboptimal treatment for this patient group
• Acute cystitis
• Pregnancy or breast-feeding
• Averse to using secure contraception with regard to men with partners and premenopausal women