Urothelial carcinomas are one of the most commonly diagnosed cancers worldwide. Postoperative patients carry a poor prognosis with an estimated five-year disease-specific survival rate of 50%. To improve overall survival and reduce the recurrent risk, chemotherapy is recommended as a standard of care. However, currently in Hong Kong, neoadjuvant (preoperational) chemotherapy and adjuvant (postoperative) chemotherapy are not commonly or regularly provided due to the concern of the potential harm from both physicians and patients. Recently, genetic signature from circulating tumor DNA (ctDNA) is emerging as a pivotal biomarker for detecting caner in early stage and molecular residual disease (MRD). With strengths of non-invasive and superior sensitivity, ctDNA is hopefully to serve as a cancer-agnostic surrogate analyte for risk stratification of tumor recurrence, thereby guiding individually tailored treatment. Therefore, this study is proposed to exploratively assess the benefit of ctDNA-guided approach for postoperative adjuvant therapy.

Inclusion Criteria:

1. aged 18-70 years old;

2. a score of ≤1 for the Eastern Cooperative Oncology Group (ECOG) Performance Status;

3. receiving radical cystectomy (with lymph node dissection) or nephroureterectomy;

4. histologically confirmed (surgical specimen) muscle invasive urothelial carcinoma, and the major histological type should be transitional cell carcinoma;

5. Classification of tumour, node and metastasis (TNM): pT2-4a N0-2M0;

6. absence of microscopic (i.e., positive margin) or gross residual of the tumor (R0 resection) and absence of metastasis, confirmed by a negative CT or MRI scan of pelvis, abdomen and chest within 4 weeks prior to enrolment;

7. adequate hematologic and end-organ function, defined by the following laboratory results obtained within 28 days prior to the first study treatment:

   • ANC≥1500 cells/μL (without granulocyte colony-stimulating factor support within 2 weeks prior to Cycle 1, Day 1)
   • WBC counts > 2500 cells/μL
   • Lymphocyte count ≥ 300 cells/μL
   • Platelet count ≥ 100,000 cells/μL (without transfusion within 2 weeks prior to Cycle 1, Day 1)
   • Hemoglobin ≥ 9.0 g/dL
   • AST, ALT, and alkaline phosphatase ≤ 2.5 × the upper limit of normal (ULN),
   • PTT ≤ 1.5 × ULN
   • PT ≤ 1.5 × ULN or INR < 1.7
   • Calculated creatinine clearance ≥ 30 mL/min (Cockcroft-Gault formula)

8. able to understand and provide written informed consent, and agree to receive the treatment arrangement and study procedures stated in the informed consent

Exclusion Criteria:

1. receiving any approved anti-cancer treatment within 3 weeks prior to study enrolment;
2. participation in another clinical trial with therapeutic intent within 28 days prior to enrolment;
3. suffering from malignancies other than urothelial carcinoma within 5 years prior to study enrolment;
4. conditions that contraindicate chemotherapy, such as renal impairment with creatinine clearance rate (CCr) <50 mL/min, hearing impairment, and inadequate marrow function;
5. anaphylactic or hypersensitivity reactions or other contraindication to cisplatin and gemcitabine;
6. active or uncontrolled infections, including human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), or tuberculosis;
7. pregnancy or breastfeeding.