Bladder cancer (BC) can be divided into two subgroups depending on invasion of the muscular layer: non-muscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC). Its aggressiveness is associated, inter alia, with genetic aberrations like losses of 1p, 6q, 9p, 9q and 13q; gain of 5p; or alterations in the p53 and p16 pathways. Moreover, there are reported metabolic disturbances connected with poor diagnosis—for example, enhanced aerobic glycolysis, gluconeogenesis or haem catabolism.Currently, the primary way of treatment method is transurethral resection of the bladder tumour (TURBT) with adjuvant Bacillus Calmette–Guérin (BCG) therapy for NMIBC or radical cystectomy for MIBC combined with chemotherapy or immunotherapy. However, intravesical BCG immunotherapy and immune checkpoint inhibitors are not efficient in every case, so appropriate biomarkers are needed in order to select the proper treatment options. It seems that the success of immunotherapy depends mainly on the tumour microenvironment (TME), which reflects the molecular disturbances in the tumour. TME consists of specific conditions like hypoxia or local acidosis and different populations of immune cells including tumour-infiltrating lymphocytes, natural killer cells, neutrophils and B lymphocytes, which are responsible for shaping the response against tumour neoantigens and crucial pathways like the PD-L1/PD-1 axis.In this review, we summarise holistically the impact of the immune system, genetic alterations and metabolic changes that are key factors in immunotherapy success. These findings should enable better understanding of the TME complexity in case of NMIBC and causes of failures of current therapies.

Introduction A tumor microenvironment plays an important role in bladder cancer development as well as in a treatment response. Purpose The aim of the study is to assess how the components of the microenvironment, in terms of cells, potentially affect tumor recurrence as well as to find the potential biomarkers for immunotherapy in NMIBC. Methods The study group consisted of 55 patients with primary NMIBC. Immunohistochemistry was performed on sections of primary papillary urothelial carcinoma of the bladder removed during transurethral resection of the tumor. Cox proportional hazard multiple regression analysis was performed to characterize tumors with the highest probability of an unfavorable outcome. Results The expression of analyzed variables was found in 90% of the examined tissues. Multivariate analysis confirmed that the CD4 (HR 1.19, 95% CI 1.07-1.32, p = 0.001), CD20 (HR 0.9, 95% CI 0.84-0.97, p = 0.008) and PD-L1 expressed on tumor cells (HR 0.05, 95% CI 0.008-0.29, p = 0.01) were independently associated with the risk of recurrence of bladder cancer. Patients with weak CD4+ cells (< 4,6%) infiltration and severe CD20+ infiltration (>10%) belong to the group with a lower risk of recurrence. The cancer in this group frequently recurs also after 12 months (p=0.0005). Conclusions The evaluation of CD4+ and CD20+ cells in the tumor microenvironment, in addition to PD-L1 on tumor cells, facilitates determination of a group of patients with a low risk of the recurrence that could also be recognized after 12 months following the primary tumor resection.