(Figure 1).
Discussion
In the present study, we observed that urinary N-methylhistamine and histamine levels were increased significantly with the onset of immunotherapy and N-methylhistamine levels were decreased significantly when immunotherapy was terminated. Although we did not find statistically significant differences between the responders and non-responders, the estimated marginal means of Pre-BCG N-methylhistamine were significantly higher in patients with NMIBC than healthy participants.
A few studies have shown valuable changes in the BCG-induced urinary immune microenvironment. In this field, IL-17+ mast cell, interleukins, TNF-α, IFN-γ, and soluble ICAM-1 levels have been examined [7, 12, 13]. But there is no available data in the literature that can clearly determine mast cell activation in patients with NMIBC treated with BCG. In our study, we determined that the urinary N-methylhistamine and histamine levels increased with BCG immunotherapy and N-methylhistamine decreased with the termination of this BCG immunotherapy. Tryptase is considered to be an unstable mast cell mediator, and therefore there was no statistically significant change in the tryptase levels due to BCG immunotherapy.
Clinically applicable tools to predict disease recurrence and progression are much needed. Studies on predicting immunotherapy response started with measuring purified protein derivative (PPD)-associated BCG response. In a study, the median recurrence-free survival was 25 months in the PPD-negative group and was not available in the PPD positive group (p < 0.05) [14]. But there was only one study about the mast cell-related immunotherapy response. [7]. This study has confirmed the predictive value of IL-17+ mast cells in patients with NMIBC treated with BCG immunotherapy, and higher numbers of IL-17+ cells have found associated with improved event-free survival. However, there is no available data in the literature to determine urinary N-methylhistamine, histamine, and tryptase levels in patients with NMIBC. In our study, the lack of a statistically significant difference between the mast cell mediators and immunotherapy response can be explained with the small size of the patient group. The quantitative differences regarding the samples suggest that statistically significant differences could be found in further studies designed with larger patient groups.
There are a few studies on urinary markers in identifying NMIBC patients. Although some studies have reported promising results in determining bladder cancer with urinary immune markers, there were no mast cell-related markers in the literature [15, 16]. In our study, increased urinary N-methylhistamine levels were found in patients with NMIBC compared to healthy participants. These results can be discussed in several aspects. The evaluation of the samples obtained at the first visit before BCG instillation in patients with NMIBC excluded the BCG-related immunological response. However, the samples were taken after the re-TUR procedure, suggesting that a resection-induced mast cell activation may have been effective. Therefore, it can be considered that resection-associated mast cell activation alone can be effective against tumor cells.
A few studies suggest that a decrease in immune system function in elderly patients may weaken the BCG response. Kanematsu et al. were the first to report significantly reduced protection from tumor recurrence and reduced tuberculin skin test reactivity in patients aged >80 years treated with BCG [17]. A phase 2 study revealed that patients older than 80 years had the poorest recurrence-free survival, and thus being over 80 was an independent predictor of recurrence (hazard ratio: 1.56) [18]. Furthermore, age also found to be an independent predictor of progression by the Club Urologico Espanol de Tratamiento Oncologico (CUETO) group [19]. Although in our study, the mean age was reported higher in immunotherapy non-responders, these differences were not found statistically significant due to the low number of patients (p = 0.098).
Despite the promising results, our study has certain limitations. First, it was a single-center study with a relatively low number of cases. Second, it is considered that increasing the number of visits could provide more detailed information about the changes in the mast cell mediators. Third, although all patients with NMIBC were high grade, excluding other clinical and pathological conditions that could affect immunotherapy response can be considered as another limitation. Future studies with larger sample size and longer follow-up are needed to predict BCG response at the beginning of the treatment.
Conclusions
This is the first study to determine that urinary N-methylhistamine and histamine levels were increased significantly with receiving immunotherapy and N-methylhistamine levels were decreased significantly when immunotherapy was terminated. Although there are no statistically significant differences between the immunotherapy responders and non-responders, the estimated marginal means of Pre-BCG N-methylhistamine levels are significantly higher in patients with NMIBC than healthy participants. These results are promising for further studies to be conducted on mast cell activation.