Background: The programmed cell death-1 (PD-1) pathway has been suggested to play an important role in tumor immune escape. We evaluated changes in PD-1 expression before and after Bacillus Calmette–Guérin (BCG) therapy and its prognostic significance in non-muscle-invasive bladder cancer (NMIBC) patients. Methods: We examined 78 paired tissue samples of NMIBC in tumors just before BCG therapy and BCG-relapsing tumors, defined as recurrence after achieving disease-free status by initial BCG instillations for 6 months. We counted PD-1-positive cells, and PD-1 expression was defined as high when the number of PD-1-positive cells was more than 18 under ×200 magnification. Results: The median number of PD-1-positive cells in tumors just before BCG therapy was 3.5, significantly lower than that in BCG-relapsing tumors (17.0, p < 0.001). High PD-1 expression was observed in 20 tumors just before BCG therapy (25.6%) and 36 BCG-relapsing tumors (46.2%). Fifty-two cases (66.6%) showed an increase in the number of PD-1-positive cells in BCG-relapsing tumors. High PD-1 expression in BCG-relapsing tumors was independently associated with subsequent tumor recurrence (p = 0.011) and stage progression (p = 0.033). The 5-year recurrence-free and progression-free survival rates were 40.7 and 74.1% in patients with high PD-1 expression in BCG-relapsing tumors, significantly lower than those in their counterparts (72.9 and 94.1%, respectively). Conclusions: PD-1 was induced by BCG therapy, and its expression in BCG-relapsing tumors may be an important indicator for predicting worse clinical outcomes in NMIBC patients treated with BCG therapy.
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