CD8+ Cell Density Gradient across the Tumor Epithelium–Stromal Interface of Non-Muscle Invasive Papillary Urothelial Carcinoma Predicts Recurrence-Free Survival after BCG Immunotherapy

SIMPLE SUMMARY: Bacille Calmette–Guerin (BCG) immunotherapy of non-muscle invasive papillary urothelial carcinoma fails in over 30% of cases. In our study, we explore the significance of tumor-infiltrating cytotoxic lymphocytes, assessed by digital analysis and computational methods measuring the cell gradient density profiles across the tumor epithelium–stroma interface, to predict recurrence-free survival in these patients. We analyzed CD8+ cell distribution profiles in the tumor tissue using previously published methods of gradient assessment (center of mass and immunodrop) along with patients’ clinical and pathology data. We found that both CD8+ cell gradient indicators were statistically significant prognosticators of recurrence-free survival, and together with clinical and pathological data might be used for improved patient risk stratification. In this context, we propose a prototypic risk assessment system incorporating pathology, patients’ history, and CD8+ cell gradient features. ABSTRACT: Background: Bacille Calmette–Guerin (BCG) immunotherapy is the first-line treatment in patients with high-risk non-muscle invasive papillary urothelial carcinoma (NMIPUC), the most common type of bladder cancer. The therapy outcomes are variable and may depend on the immune response within the tumor microenvironment. In our study, we explored the prognostic value of CD8+ cell density gradient indicators across the tumor epithelium–stroma interface of NMIPUC. Methods: Clinical and pathologic data were retrospectively collected from 157 NMIPUC patients treated with BCG immunotherapy after transurethral resection. Whole-slide digital image analysis of CD8 immunohistochemistry slides was used for tissue segmentation, CD8+ cell quantification, and the assessment of CD8+ cell densities within the epithelium–stroma interface. Subsequently, the gradient indicators (center of mass and immunodrop) were computed to represent the density gradient across the interface. Results: By univariable analysis of the clinicopathologic factors, including the history of previous NMIPUC, poor tumor differentiation, and pT1 stage, were associated with shorter RFS (p < 0.05). In CD8+ analyses, only the gradient indicators but not the absolute CD8+ densities were predictive for RFS (p < 0.05). The best-performing cross-validated model included previous episodes of NMIPUC (HR = 4.4492, p = 0.0063), poor differentiation (HR = 2.3672, p = 0.0457), and immunodrop (HR = 5.5072, p = 0.0455). Conclusions: We found that gradient indicators of CD8+ cell densities across the tumor epithelium–stroma interface, along with routine clinical and pathology data, improve the prediction of RFS in NMIPUC.