|Key inclusion criteria|
| • Age ⩾18 years.|
• Patients with primary or recurrent multiple histologically confirmed Ta or T1 (non-muscle invasive), G1 or G2 (low-grade) urothelial carcinoma of the bladder with no evidence of carcinoma in situ.
• Patients must have at least 2 lesions, but no more than 10.
• The resected lesions must contain detrusor muscle to confirm a Ta/T1 disease.
• All visible lesions must be completely removed by transurethral resection at entry to the study, except for an untouched marker lesion measuring 0.5–1.0 cm in its greatest dimension.
• Bimanual examination immediately following transurethral resection under anaesthesia should be carried out and no mass should be felt.
• Adequate renal function (creatinine < 150 μmol/L and/or an eGFR > 60 ml/L).
• Adequate liver function (bilirubin < 1.5 times upper limit of normal, ALAT or ASAT < 2.5 the upper limit of normal).
• Eligible patients must be fully informed of the investigational nature of the study and written signed informed consent must be obtained prior to any study specific investigations.
• Mentally, physically, and geographically able to undergo treatment and follow up.
|Key exclusion criteria|
| • Patients having muscle-invasive disease (stage T2 or greater) or CIS.|
• Patients with grade 3 (high-grade) tumours.
• Patients with diabetes mellitus receiving metformin or having received metformin in the past 6 months.
• Patients who have received intravesical treatment (chemotherapy or immunotherapy) within the last 3 months.
• Patients that are currently receiving other anti-cancer therapy.
• Patients with existing urinary tract infection or recurrent severe bacterial cystitis.
• Patients that need to be treated with a transurethral catheter.
• Patients with urogenital tumours with histology other than urothelial carcinoma (i.e., squamous cell or adenocarcinoma) or with urothelial carcinoma involving the upper tract or the prostatic urethra.
• Patients with a history of other primary malignancy (other than squamous or basal cell skin cancers or cone biopsied CIS of the uterine cervix or prostate carcinoma treated curatively with normal PSA values at inclusion) in the last five years.
• Patients with active, uncontrolled impairment of the renal, hepatobiliary, cardiovascular, gastrointestinal, urogenital, neurologic or hematopoietic systems that, in the opinion of the investigator, would predispose to the development of complications from the administration of metformin.
• Patients who are using loop diuretics, cimetidine, ranitidine, cetirizine, trimethoprim, vandetanib, kinidine and/or anti-HIV medication (due to drug interactions), for which no reasonable alternative is available.
• Women who are pregnant or lactating. Individuals of reproductive potential may not participate unless agreeing to use an effective contraceptive method for themselves and/or their sexual partner.
• Patients with ECOG-WHO performance status of 3 or 4.
• Patients with a known history of alcohol abuse.
• Patients with a known hypersensitivity to metformin.
• Patients who in the investigator’s opinion, cannot comply with provisions of the protocol or do not understand the nature of the study.