This prospective observational cohort study aims to evaluate the association between intraoperative irrigation fluid absorption and perioperative cell-free DNA (cfDNA) dynamics in patients undergoing transurethral resection of bladder tumor (TURBT). Eligible patients with suspected or confirmed bladder cancer scheduled for TURBT will be enrolled. Intraoperative irrigation fluid absorption volume will be recorded, and peripheral blood samples will be collected before surgery and within 24 hours after surgery for cfDNA extraction and mutation analysis.

The study will assess whether irrigation fluid absorption volume is associated with changes in cfDNA concentration, tumor-related mutation detection, and clinicopathological features, including tumor stage, grade, size, number, invasion depth, concomitant carcinoma in situ, operative time, resection depth, and intraoperative blood loss. Patients will also be followed for postoperative recurrence, progression, metastasis, and other adverse oncological outcomes.

This study may provide preliminary evidence for understanding perioperative tumor-related molecular changes during TURBT and may help improve risk stratification, perioperative management, and postoperative follow-up strategies for patients with bladder cancer.

Bladder cancer is one of the most common malignancies of the urinary system. Non-muscle-invasive bladder cancer accounts for the majority of newly diagnosed cases. Transurethral resection of bladder tumor (TURBT) is the standard procedure for the diagnosis, staging, and initial treatment of bladder cancer, particularly non-muscle-invasive bladder cancer. However, postoperative recurrence and progression remain common in some patients, especially those with high-risk pathological features.

During TURBT, mechanical resection, electrosurgical thermal injury, and continuous bladder irrigation may lead to tumor cell shedding and the release of tumor-derived molecular components into the irrigation fluid. Disruption of the mucosal and vascular barriers, opening of venous sinuses, increased intravesical pressure, and absorption of irrigation fluid may theoretically facilitate the entry of tumor-related components into the circulation. Although previous studies have mainly focused on intravesical tumor cell implantation and local recurrence, the relationship between intraoperative irrigation fluid absorption, perioperative cfDNA dynamics, and postoperative oncological outcomes remains insufficiently understood.

In this prospective observational cohort study, patients undergoing TURBT for suspected or confirmed bladder cancer will be enrolled. Intraoperative irrigation fluid absorption volume will be measured and recorded. Peripheral blood samples will be collected before surgery and within 24 hours after surgery for cfDNA extraction and mutation analysis using a multiplex mutation detection system based on nucleic acid mass spectrometry. Tumor tissue mutation status will also be evaluated when available.

The primary objective is to determine whether the volume of intraoperative irrigation fluid absorption is associated with perioperative changes in plasma cfDNA levels and tumor-related mutation detection. Secondary objectives include evaluating the association of cfDNA dynamics and irrigation fluid absorption with clinicopathological characteristics, including tumor stage, grade, size, number, invasion depth, concomitant carcinoma in situ, operative time, resection depth, and blood loss. Postoperative recurrence, progression, metastasis, and other adverse oncological outcomes will be assessed during follow-up.

The study is observational and will not alter standard clinical treatment decisions. The findings may help clarify perioperative molecular changes associated with TURBT and provide preliminary evidence for improving risk stratification and individualized postoperative surveillance in patients with bladder cancer.

Inclusion Criteria:

1. Age 18 years or older.
2. Suspected or histologically confirmed urothelial carcinoma of the bladder.
3. Scheduled to undergo TURBT.
4. Availability of sufficient peripheral blood samples for cfDNA extraction and mutation analysis.
5. Availability of complete clinicopathological and perioperative data.
6. Ability to provide informed consent and comply with study follow-up.

Exclusion Criteria:

1. Non-urothelial bladder malignancy confirmed by pathology.
2. History of other malignant tumors within the past 5 years, except adequately treated non-melanoma skin cancer or carcinoma in situ of the cervix.
3. Previous radical cystectomy or systemic antitumor therapy before enrollment.
4. Inadequate blood sample quality or insufficient DNA yield for mutation analysis.
5. Pregnancy or breastfeeding.
6. Serious uncontrolled intercurrent illness that may interfere with study participation, follow-up, or compliance, including active infection, symptomatic congestive heart failure, unstable angina, clinically significant arrhythmia, severe psychiatric illness, or other conditions judged by the investigator to make participation unsuitable.

This study will include adults aged 18 years or older with suspected or confirmed bladder urothelial carcinoma who are scheduled to undergo TURBT at the Second Hospital of Lanzhou University. Eligible participants must be able to provide sufficient peripheral blood samples for cfDNA extraction and mutation analysis. Postoperative pathological diagnosis will be used to confirm eligibility for the final analysis when applicable. Patients will receive standard clinical management, and participation in this observational study will not affect treatment decisions.

The possibility of sharing de-identified individual participant data will be evaluated after study completion. Any future data sharing will depend on the scope of informed consent, institutional policies, ethics approval requirements, and the establishment of appropriate data use agreements. Shared data, if available, will not contain personally identifiable information.