Prostate cancer, the most common non-cutaneous malignancy prevalent in males, is the 2^nd leading cause of death compared to other cancers in men [1]. Radical prostatectomy is one of the treatment options available for organ-confined disease. Postoperative incontinence is a common side effect after prostatectomy that can severely impact quality of life [2-6]. The pathophysiology of incontinence is largely due to extrinsic sphincter insufficiency; however may be exacerbated by various other factors [7].

As divulged by a recent review of the literature, other factors such as detrusor overactivity, reduced bladder capacity, and impaired detrusor contractility can be pivotal for developing bladder dysfunction after prostatectomy [8]. Moreover, de novo detrusor instability after prostatectomy can lead to overactive bladder (OAB) symptoms, which may be detectable by urodynamic evaluation [9]. Currently, lack of the knowledge on the preoperative biomarkers alluding to postoperative incontinence is a limiting factor in the counseling process because the information may potentially be used as an additional component at the time of counseling. To this end, a previous study using a proteomics chip based analysis of urinary cytokine expression demonstrated that OAB group expressed Monocyte Chemotactic Protein-1 (MCP-1) two-fold higher than UTI population and controls, thus suggesting MCP-1 to be a potential target for an OAB biomarker [10]. Based on these premises, we conducted a clinical study to assess whether urinary MCP-1 can be a potential preoperative biomarker associated with the outcome of 30-day urinary continence after robotic radical prostatectomy (RRP).

After exclusions, 76 patients were included in analyses. Demographics of the group are presented in Table 1. Approximately in 80% (61/76) of cases, patients followed the log or sent post cards of their zero pad date, while remaining 20% (15/76) patients were contacted by either telephone or email. The primary outcome of continence consisting of using zero pads was reached by 29% (22/76), 56% (42/76), and (75/76) 98% at 7, 30, and 60 days, respectively. Comparing incontinent and continent men at 30 days after prostatectomy, the IPSS score (7.7 vs. 6.1; p=0.237), urgency question (1.5 vs. 1.1; p=0.283), or quality of life question (1.0 vs. 0.7; p=0.317) were not associated with urinary continence. The urgency question (none=0 vs. any =1) of the IPSS score did not demonstrate any association with time to urinary continence (36 vs. 34 days; p=0.858). Furthermore, the correlations between MCP1 and other variables were investigated. Of note, the urinary creatinine (r=0.21; p<0.001) and the total bladder volume (r=-0.56; p<0.001) showed the highest correlation with MCP-1. Because creatinine excretion may vary due to diurnal creatinine production, physical activity, emotional stress, diet, muscle mass (hence age, sex, and body weight variation), and disease state, we chose to correct the MCP-1 value using the better correlative value of total urine volume, and then accounted for creatinine in multivariable analysis [13]. Other variables significantly correlated with MCP-1 include the sexual health inventory for men (IIEF-5; r=-0.24; p=0.037) and the American Urological Association symptom score (IPSS; r=0.25, p=0.030). No significant correlations were identified between MCP-1 and other demographic variables.

We investigated the associations with 30 day continence in univariant analysis (Table 1). We identified no significant difference in 30-day continence between the average MCP-1(p=0.258) or MCP after adjusting for bladder volume (MCP1/TV; p=0.14). Additionally, bladder volume was larger in those who were continent at 30 days but was not statistically significant (482 vs. 397, p=0.098). We then analyzed MCP by quartiles and comparing the highest quartile of MCP-1 (MCP > 166 pg/mL) to all other quartiles, we noted a delay in continence(p=0.050). Subsequently, we normalized MCP-1 values by dividing them by the total bladder volume (TV, mL) and obtained the highest quartile (MCP-1 >0.53). Comparing MCP-1/TV to all other quartiles, we again noted a significant delay in continence among patients with the highest quartile. At 30 days only 26% (5/19) in the highest MCP1/TV quartile were continent, whereas 65% (37/57) of men in the 3 lower quartile reached zero pad continence(p=0.003) (Fig 1). Additionally, men in the highest MCP-1/TV quartile were also noted to have significantly higher incontinence at 7 days (89.5% vs. 64.9%; p=0.041) compared to all other quartiles combined. At 60 days, the difference in continence rates for highest quartile of MCP1/TV vs. lower quartiles (68.4% vs. 78.9%; p=0.350) was no longer statistically significant.

Fig. (1). Bar graph representing zero pad continence at selected time points for the highest quartile MCP-1/TV.

Next, a logistic regression model was developed including MPC1/TV (highest quartile vs. lower quartiles), and IIEF-5 as independent variables in the model. In addition, urinary creatinine was included in the model to account for urine concentration and bilateral nerve sparing was included as it trended to significance in univariant analysis. We noted that patients in the highest quartile of MCP-1/TV bear a significant risk of being incontinence at 30 days from robotic prostatectomy which is controlling other factors (OR 0.22; 95% CI 0.058-0.80; p=0.022) (Table 2).

To summarize, our studies indicate that high preoperative levels of Monocyte chemotatic protein-1 corrected for total bladder volume may play a role in developing incontinence at 30 day. These findings further suggest that a preconditioned state of high inflammation may be present in some patients causing bladder pathology thus contributing to prolonged recovery of continence. Indeed our previous study leading to this investigation postulated that elevated expression of MCP-1 in patients with overactive bladder could contribute to incontinence [10]. Another important aspect of our investigation is the pinning down MCP-1/TV as a potential biomarker to identify subjects that can start medications early in the recovery process. It is expected that such patients may benefit more from OAB therapy prior to prostatectomy .

At present, studies are indeed limited regarding anti-inflammatory therapy to prevent post-operative incontinence. However, rising interest in MCP-1 as a diagnostic or therapeutic target in other diseases may provide such opportunity. It will be quite prudent to undertake studies to test whether the ablation of MCP-1 prior to radical prostatectomy will diminish the extent of urinary incontinence. It is worth mentioning that CCR2 (chemokine receptor 2), which is the primary MCP-1 receptor, has been considered to be an important therapeutic target in treating the deleterious effects of myocardial infarction and acute kidney injury [14, 15]. Likewise, the same mechanism may be tested in a pre-prostatectomy cohort investigating urinary outcomes. Another evolving concept regarding reducing inflammation is hypothermia of the prostate via a rectal balloon at the time of surgery [16]. Our previous study is quite remarkable because all patients who received hypothermia during prostatectomy, had a significant reduction in post prostatectomy incontinence [17]. However, in this pilot study, we were unable to determine the true effect of hypothermia, specifically on MCP-1 because we did not measure intraoperative or postoperative MCP-1 levels.

Currently, surgeons are compelled to assess the bladder symptoms of the patients by using demographics and questionnaires prior to prostatectomy due to the lack of any specific biomarkers. In line with this, a systematic review and meta-analysis of post-prostatectomy incontinence reported associations with age, BMI >30, comorbidities, severity of lower urinary tract symptoms, and preoperative erectile function (IIEF-5) [18]. We also investigated these variables in our cohort and noted preoperative sexual function (IIEF-5) to be an exclusive albeit significant determinant of incontinence. To the contrary, our studies do not conform to the notion that one of the most significant factors for incontinence is the age of the patient. Our study enrolled many men of similar age group and revealed that age difference exerts a negligible effect on the incontinence in this study population [19]. Other preoperative indicators have been examined including ultrasound of pelvic muscles and MRI of membranous urethral length, however these would add to the current cost and may rely on other specialists [20, 21]. In all, a urinary biomarker, such as MCP-1 would be valuable because this could provide uniform, objective risk profile that may be used across various sites. At this stage, a larger study potentially in the context of a clinical trial to confirm the results of MCP-1 as a urinary biomarker to predict post-operative continence is further warranted. The information obtained from such a biomarker could weigh heavily in the discussion regarding radical prostatectomy expectations and an individualized treatment plan, which may include pre-operative pelvic therapy and early use of medications.

We are aware of the limitations of this study because of the small sample size and homogeneous nature of our population especially in the context of age and race/ethnicity. We specifically chose to use strict entry criteria for this pilot study to show proof of concept and obtain preliminary data to justify inclusion into a clinical trial. Additionally, urinary biomarkers can indicate substantial variability from day to day, hydration status, and a multitude of other factors [22]. We limited the evaluation of urinary biomarkers for post prostatectomy solely to MCP-1. However, we plan to further investigate other urinary biomarker such as nerve growth factor that has been demonstrated to be promising for detrusor over-activity [23]. Further study would need to seriously test preoperative MCP-1 at various time points prior to surgery and changes noted post operatively. Of note, the origin and causality of MCP-1 are beyond the scope of this study. In this pilot study, we did not deploy urodynamics peri-operatively to identify exact type of urinary incontinence. Overall, we feel the prospective nature and the addition of bladder volume are novel in post-prostatectomy incontinence.

In addition to other factors, high levels of Monocyte chemotactic protein - 1 may be associated with delayed recovery of continence after radical prostatectomy. Comprehensively, additional investigations are absolutely critical to establish MCP-1 as a urinary biomarker to predict delayed post-prostatectomy continence preoperatively. Based on these premises we infer that further studies with lager and broader populations are pivotal for confirmation of the findings presented in this report.