• Aged ≥18 years at the time of signing informed consent.

• Able to give written informed consent.

• Have biopsy-proven low-grade upper tract urothelial cancer (LG-UTUC) confirmed by a pathology report ≤2 months prior to enrolment.

• Have ≥1 measurable papillary low-grade tumour (5-15 mm in maximum diameter), evaluated visually above the ureteropelvic junction before enrolment.

‣ Subjects with low-grade tumour larger than 15 mm will be eligible if endoscopic downsizing of the tumour to 5-15 mm in maximum diameter has been performed before enrolment.

• Willing to be available for at least 18 months after first dosing.

• Have life expectancy \>2 years, in the opinion of the investigator.

• Have an Eastern Cooperative Oncology Group (ECOG) status of 2 or less.

• Females of reproductive potential must have a negative highly sensitive urine or serum pregnancy test upon entry into this trial and be willing to use highly effective contraception during treatment with the investigational medicinal product (IMP) and for 6 months following the last dose. Otherwise, female subjects must be postmenopausal (no menstrual period for a minimum of 12 months) or surgically sterile. Highly effective methods of contraception include: combined (oestrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal or transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable or implantable), intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner, and sexual abstinence.

• Male subjects with female partners of reproductive potential must be surgically sterile or willing to use a condom in addition to effective contraception in their female partner during treatment with the IMP and for 3 months following the last dose.

⁃ Adequate laboratory values:

∙ haemoglobin ≥10 g/dL

‣ white blood cells (WBC) ≥4000/μL

‣ absolute neutrophil count (ANC) ≥2000/μL

‣ platelet count ≥100,000/μL

‣ international normalized ratio (INR)\* below institutional upper limit of normal (ULN)

‣ activated partial thromboplastin time (aPTT)\* below institutional ULN

‣ aspartate aminotransferase (AST) ≤1.5 x ULN

‣ alanine aminotransferase (ALT) ≤1.5 x ULN

‣ total bilirubin ≤1.5 x ULN

‣ sodium \>135 mmol/L

‣ potassium between 3.6 and 5.0 mmol/L

⁃ Have an estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73 m2 (for inclusion in the safety lead-in the eGFR must be ≥60 mL/min/1.73 m2 \[see exclusion criteria #20\]).