Fibroblast Activation Protein-α and the Immune Landscape: Unraveling T1 Non-muscle-invasive Bladder Cancer Progression.

Background And Objective: The tumor microenvironment (TME) in non-muscle-invasive bladder cancer (NMIBC) plays an important role in the anticancer response. We aimed to identify the prognostic biomarkers in the TME of patients with NMIBC for progression to ≥T2.

Methods: From our institutional database, 40 patients with T1 high-risk NMIBC who progressed were pair matched for Club Urologico Español de Tratamiento Oncologico (CUETO) progression variables with 80 patients who never progressed despite longer follow-up. Progression was defined as ≥T2 or extravesical disease. Patients were treated at least with bacillus Calmette-Guérin (BCG) induction (five or more of six doses). Immunohistochemical (IHC) markers for the TME were used on tissue at first T1 diagnosis: CD8-PanCK, GZMB-CD8-FOXP3, CD163, PD-L1 SP142/SP263, fibroblast activation protein-α (FAP), and CK5-GATA3. Full tissue slides were annotated digitally. Relative marker area (IHC-positive area/total area) or density (IHC-positive cells per area; /mm) was calculated, differentiating between regions of interest (ROIs; T1, Ta, and carcinoma in situ) and between compartments (stromal, epithelial, and combined). Differences in IHC variables were assessed using the test, for continuous variables using analysis of variance and comparisons of more than two groups using Tukey's test. Conditional logistic regression for progression at 5-yr follow-up was performed with clusters based on pair matching.

Key Findings And Limitations: Only FAP expression (increase per 50%) in T1 (odds ratio [OR]: 1.33; 95% confidence interval [CI]: 1.04-1.70) and all ROIs combined (OR: 1.62; 95% CI: 1.14-2.29) correlated significantly with progression. None of the other clinicopathological/IHC variables correlated with progression.

Conclusions And Clinical Implications: FAP is a potential prognostic biomarker for progression in high-risk NMIBC. FAP is a marker for cancer-associated fibroblasts and is linked to immunosuppression and neoangiogenesis, which makes future investigation clinically relevant.

Patient Summary: We found that progression of high-risk non-muscle-invasive bladder cancer to muscle-invasive disease is less in patients with lower fibroblast activation protein-α (FAP) expression, which is a marker for cancer-associated fibroblasts.