Differential Expression of PD-L1 in High Grade T1 vs Muscle Invasive Bladder Carcinoma and its Prognostic Implications

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Abstract
PD-L1 is expressed on tumor cells and tumor immune cell infiltrates. In metastatic bladder cancer increased tumor immune cell infiltrate PD-L1 positivity correlated with better overall survival. However, to our knowledge in high grade T1 bladder tumors positivity on tumor cells and tumor immune cell infiltrates, and correlation with outcomes or pathological features remain unknown. Formalin fixed, paraffin embedded tumor samples from 140 patients with clinically annotated, high grade T1 bladder tumors were retrieved. All patients were initially diagnosed with high grade T1 bladder tumors by transurethral resection, subsequently received bacillus Calmette-Guérin and had a median followup of 7.4 years. PD-L1 positivity on initial transurethral resection was evaluated by immunohistochemistry using a mouse monoclonal antiPD-L1 antibody (405.9A11). Tumor cell PD-L1 positivity was defined as staining of 5% of the tumor cell membrane. Tumor immune cell infiltrate PD-L1 positivity was scored based on the extent of infiltrate and the percent of positive cells. The Fisher exact test was used to assess associations of PD-L1 positivity with disease outcomes, carcinoma in situ presence and the difference between high grade T1 bladder tumors and muscle invasive bladder cancer. Among 140 patients with high grade T1 bladder tumors tumor cells and tumor immune cell infiltrate PD-L1 positivity was seen in 6 (4%) and 48 (34.3%), respectively. In a subset of 106 patients with adequate followup PD-L1 positivity did not correlate with disease outcomes on tumor cells (p = 0.3) or on tumor immune cell infiltrates (p = 0.47). PD-L1 positivity also did not correlate with the presence of carcinoma in situ. Tumor cell PD-L1 positivity was significantly less in high grade T1 bladder tumors than in muscle invasive bladder cancer (p <0.001). PD-L1 is widely expressed on tumor immune cell infiltrates but not on tumor cells in high grade T1 bladder tumors. We did not find a correlation between PD-L1 positivity and outcomes or carcinoma in situ presence. Tumor cell PD-L1 positivity is significantly lower in high grade T1 bladder tumors than in muscle invasive bladder cancer.

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