(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.