en Cancer Cancer Original Article Original Article <span style="font-family:Tahoma;"><span style="font-size:12px;"><span style="unicode-bidi:embed"><span style="line-height:107%">Treatment failure after intravesical instillation of Bacillus Calmette-Guerin immunotherapy (BCG) for non-muscle-invasive bladder cancer (BCa) occurs frequently. The exact effects of BCG on cellular redox status and gene expression remain unclear. We assessed oxidative stress biomarkers and changes in miR-155-5p expression in response to BCG. Twenty-seven patients with BCa were recruited for measuring tissue and serum malondialdehyde (MDA) and total antioxidant capacity (TAC) levels, and tissue expression of miR-155-5p at two-time points: pre and 6 weeks post BCG. Recurrence of BCa was observed after 20 months. R statistical software was used for paired comparisons of biomarkers, as well as the correlation between variables. Significant increases in TAC were observed after BCG (P= <0.001). Tissue MDA levels were significantly reduced (P= 0.003). miR-155-5p was slightly overexpressed after BCG (median fold change=1.3, P=0.25). At the 20-month follow-up, it was observed that improved MDA and TAC changes were significant only in patients without recurrence of BCa. In patients with recurrence, the pre-treatment expression ratio of miR-155-p5 was positively correlated with TAC (R=0.63, P= 0.032) and negatively correlated with MDA (R=-0.72, P=0.037). In patients with recurrence of BCa pre-treatment miR-155-5p showed negative correlation with its expression changes after BCG (R=-0.78, P=0.004). Conclusions: Treatment with BCG has some beneficial effects on the oxidative stress status, which is probably modulated by miR-155-5p. A well-controlled oxidative balance may enhance overall survival of BCa. Considering its high recurrence rate, our pilot experiment can open a window toward better management of patients with BCa<span dir="RTL" lang="FA">.</span></span></span></span></span> Bacillus Calmette-Guerin, bladder cancer, malondialdehyde , miR-155-5p, total antioxidant capacity 186 197 http://ijmcmed.org/browse.php?a_code=A-10-5129-1&slc_lang=en&sid=1 Mohammad Mehdi Darzi Samandarzi@yahoo.com 100319475328460030476 100319475328460030476 No Student Research Committee, Babol University of Medical Sciences, Babol, Iran. Nahid Neamati nahidneamati60@gmail.com 100319475328460030477 100319475328460030477 No Cancer Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Farzin Sadeghi sadeghi.farzin@yahoo.com 100319475328460030478 100319475328460030478 No Cellular and Molecular Biology Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Ali Bijani alibijani@yahoo.com 100319475328460030479 100319475328460030479 No Social Determinants of Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Emadoddin Moudi emadmoudi@gmail.com 100319475328460030480 100319475328460030480 Yes Clinical Research Development Center, Shahid Beheshti Hospital, Babol University of Medical Sciences, Babol, Iran.