To investigate the clinical impact of the purified protein derivative (PPD) skin test prior to bacillus Calmette-Guérin (BCG) therapy in patients with non-muscle-invasive bladder cancer (NMIBC) treated with adjuvant BCG therapy.

A total of 498 NMIBC patients treated with adjuvant BCG therapy were included, among which 320 received the PPD skin test 1 to 2 weeks prior to BCG therapy. Oncological outcomes and the rate of BCG-related side effects were statistically evaluated.

The 5-year recurrence-free survival rates of patients who received the PPD skin test or not were 66.6±2.8% and 59.1±4.1%, respectively, with a significant difference (p=0.048). No significant difference was observed in progression-free survival rates between patients who received the PPD skin test or not. Multivariate Cox regression analysis revealed that a history of recurrence (hazard ratio: HR 1.59, p=0.02), multiple tumors (HR 1.95, p<0.01), the BCG Connaught strain (HR 0.71, p=0.04), the number of BCG instillations of ≥7 (HR 0.70, p=0.04) and receiving the PPD skin test (HR 0.72, p=0.04) were independently associated with tumor recurrence. The rates of major BCG-related side effects in patients who received the PPD skin test or not were 24.1% (77/320) and 15.2% (27/178), respectively, with a significant difference (p=0.02).

The PPD skin test prior to BCG therapy enhances therapeutic effects with BCG therapy and potentially results in a higher incidence of major BCG-related side effects. Combination therapy using BCG with the PPD skin test may improve the oncological outcomes of BCG therapy.