Non-muscle invasive bladder cancers (NMIBC) constitute approximately 75% of bladder cancer cases. Primary transurethral resection (TUR) plays a pivotal role in both diagnosis and treatment. However, despite initial resection, tumors are often missed, leaving behind microscopic residual tumors. This study aims to prospectively investigate the surgical margins of tumors, which may serve as a potential source of residual tumors.

Seventy patients diagnosed with NMIBC who underwent primary TUR were enrolled in this study. Following initial resection, samples were collected from the normal-appearing mucosa extending 1cm beyond the surgical margins. Lesions were categorized as ‘healthy margins’ for benign lesions, ‘tumoral margins’ for urothelial cancer, and ‘dysplastic margins’ for urothelial dysplasia. Clinical and pathological features of these groups were compared, and risk factors for detecting transitional cell carcinoma (TCC) in the normal-looking mucosa were analyzed.

The tumoral margins group showed a significantly higher rate of T1 stage tumors compared to the healthy margins group, and a significantly higher rate of high-grade (HG) tumors compared to the dysplastic margins group. Moreover, the tumoral margins group had a significantly higher proportion of high-risk patients (85.7%) compared to the other groups, while the healthy margins group had a significantly higher proportion of low-risk patients (35.3%) compared to the tumoral margins group (0.0%). Additionally, the tumoral margins group demonstrated a significantly higher rate of carcinoma in situ (CIS) compared to the healthy margins group (35.7% vs. 5.9%). Detection of urothelial cancer at the margins was associated with T1 stage, HG stage, and the presence of CIS based on univariate analyses.

To minimize residual tumors and prevent recurrence in patients undergoing primary TUR, we advocate for the resection of macroscopically visible tumors with nearly 2cm of intact bladder tissue, thereby enhancing the quality of TUR.

This study provides Level II evidence, based on its design as a prospective observational study. The findings are derived from well-designed cohort analyses, providing significant associations and insights into the factors affecting surgical margins in NMIBC patients.