The role of tumor-infiltrating lymphocytes and depth of invasion in T1 bladder cancer: a retrospective analysis.

Background: Tumor-infiltrating lymphocytes (TILs) are integral components of the tumor microenvironment and have been extensively studied across various cancers. In bladder cancer, the prognostic significance of TILs remains uncertain. This study aimed to analyze the impact of muscularis mucosa invasion and TILs ratios on clinical outcomes, tumor aggressiveness, and prognosis in pT1 urothelial carcinoma of the bladder.

Methods: This retrospective study included 154 patients with pT1 bladder urothelial carcinoma, categorized into pT1a and pT1b groups based on the extent of muscularis mucosa invasion. TILs ratios were stratified into three groups: <1%, 1-5%, and > 5%. Clinical and pathological characteristics, including tumor diameter, necrosis, tumor thickness, recurrence, and progression rates, were compared. Depth of invasion and tumor features were assessed using standard histopathological methods. Recurrence and progression-free survival (PFS) were evaluated during a median follow-up of 20 months.

Results: By definition, pT1b tumors demonstrated significantly deeper invasion into the muscularis mucosa (p < 0.0001) compared to pT1a tumors. They were also associated with larger tumor diameter (p = 0.023), greater tumor thickness (p < 0.0001), and increased necrosis (p = 0.0012). Radical cystectomy was performed more frequently in pT1b patients (19.2%) than in pT1a patients (7.9%), although recurrence and PFS rates did not differ significantly between the groups. Higher TILs ratios were linked to increased tumor thickness (p = 0.0299) and more extensive invasion into TURBT chips (p = 0.0025), but no significant differences in recurrence or PFS rates were observed across TILs groups.

Conclusions: Muscularis mucosa invasion is a defining feature of pT1b bladder cancer and serves as a key indicator of tumor aggressiveness. While TILs were associated with aggressive tumor characteristics, their prognostic role remains inconclusive. These findings highlight the need for aggressive management strategies for pT1b disease and underscore the importance of further research into the complex interplay between TILs and tumor progression in bladder cancer.