Purpose: Bladder cancer recurrence following cystectomy remains a significant cause of bladder cancer specific mortality. Residual cancer cells contribute to cancer recurrence due to tumor spillage or undetectable preexisting micrometastatic tumor clones. We detected and quantified residual cancer cells in pelvic washing using ultradeep targeted sequencing. We compared the levels of residual cancer cells with clinical variables and cancer recurrence.
Materials and methods: The primary tumor specimen was available in 17 patients who underwent robot-assisted radical cystectomy. All tumors had negative surgical margins. Pelvic washes and blood were collected intraoperatively before and after robot-assisted radical cystectomy, after pelvic lymph node dissection and in the suction fluid collected during the procedure. Two-step sequencing, including whole exome sequencing followed by ultradeep targeted sequencing (× greater than 50,000), was done to quantify residual cancer cells in each sample. Eight patients were excluded from study due to sample quality issues. The final analysis cohort comprised 9 patients. The residual cancer cell level was quantified for each sample as the relative cancer cell fraction and compared between time points. The peak relative cancer cell fraction of each patient was correlated with clinical and pathological variables.
Results: Residual cancer cells were detected in approximately half of the pelvic washing specimens during or after but not before robot-assisted radical cystectomy. Higher residual cancer cell levels were associated with aggressive variant histology and cancer recurrence. Verifying the feasibility of using residual cancer cells as a novel biomarker for recurrence requires larger cohorts.
Conclusions: Detection of residual cancer cells in intraoperative peritoneal washes of patients with bladder cancer who undergo radical cystectomy may represent a robust biomarker of tumor aggressiveness and metastatic potential.
Keywords: cystectomy; neoplasm; neoplasm metastasis; residual; urinary bladder neoplasms; whole exome sequencing.