Use of metallic and polymeric ureteral stents in malignant ureteral obstruction

Abstract Background Malignant ureteral obstruction (MUO) is often caused by advanced intra‐abdominal cancers. Effective management must be attempted, but the treatment policy is unclear. Metallic ureteral stents are one of the latest options in managing MUO. Metallic ureteral stents are superior to traditional polyurethane stents. The present study retrospectively reviewed our four institutions’ experiences with treating MUO using metallic ureteral stent. Methods A total of 45 patients who required metallic ureteral stent placement for MUO at Yokohama City University Medical Center (Yokohama, JAPAN) between January 2014 and May 2016 were analyzed. We defined stent failure as having to change the ureteral stent before the scheduled ureteral stent exchange time or having to perform percutaneous nephrostomy (PCN). Complications were defined as an unscheduled hospital visit or hospitalization caused by incompatibility, infection, and pain of the metallic ureteral stent, etc., unrelated to the primary disease. We compared stent failure and the overall survival (OS) between metallic and polymeric ureteral stents. To evaluate the workload of the medical staff, we used the NASA Task Load Index (NASA‐TLX) in a total of 11 urologists. Results During the observation period, 8 (17.8%) patients in the metallic ureteral stent group and 10 (27.8%) in the control group developed stent failure. Complications were noted in 14 (31.1%) patients in the metallic ureteral stent group and 15 (41.7%) patients in the control group. A Kaplan–Meier analysis and log‐rank test showed no significant differences between two groups in the overall survival (P = 0.673). One or more complications developed in 19 (32.2%) patients in the metallic ureteral stent group and 18 (38.3%) patients in the control group (P = 0.409). Renal dysfunction after the replacement of the ureteral stent developed in 9 (15.3%) patients in the metallic ureteral stent group and 14 (29.8%) patients in the control group. No patients developed a urinary tract infection (UTI) that required hospitalization in the metallic ureteral stent group, whereas 3 (6.4%) patients in the control group had a UTI that was treated with hospitalization. The average workload score in the six subscales was analyzed, and the scores for mental demand and performance were higher in the metallic ureteral stent group, although there was no significant difference between the metallic and polymeric ureteral stent groups. Conclusions Metallic ureteral stents showed favorable ureteral stent patency and reduced the workload for urologists.


| BACKG ROU N D
Malignant ureteral obstruction (MUO) is often caused by advanced intra-abdominal cancers. Effective management must be attempted, but the treatment policy is unclear. [1][2][3][4][5][6][7] The current management options are retrograde ureteral stent (RUS) placement or percutaneous nephrostomy under local anesthesia. RUS is usually considered as the first treatment choice because of its low invasiveness.
However, the stent failure rate is high, with a mean failure rate of 12.2%-34.6%, [8][9][10][11][12][13] and stents must be exchanged every 3 months. 14 Resonance metallic ureteral stents (Cook Medical, Bloomington, IN, USA) are one of the latest options for managing MUO. Metallic ureteral stents are superior to traditional polyurethane stents (hereafter called "polymeric ureteral stents") with respect to endurance against external force and frequency of exchange procedures. 15 Indeed, metallic stents need be replaced only once a year, which can improve patients' quality of life and relieve the workload of medical staff. Some authors have reported the outcomes of metallic ureteral stents and the risk factors of stent failure, including prior radiotherapy, genitourinary cancer (GU) cancer, and urinary tract infections (UTIs). 16,17 Po-Ming et al. said that metallic stents provide a longer functional duration than polymeric ureteral stents and should be offered as an option for internal drainage. 18 However, few studies have compared the complications and cost. And no study examined the stress of metallic ureteral stenting procedure for urologist.
The present study retrospectively reviewed our four institutions' experiences with treating MUO using metallic ureteral stents especially in tolerance of metallic stent and work load for stenting procedure. and May 2016 were also analyzed ( Table 1) ureteral stent group, whereas 3 (6.4%) patients in the control group had a UTI that was treated with hospitalization. The average workload score in the six subscales was analyzed, and the scores for mental demand and performance were higher in the metallic ureteral stent group, although there was no significant difference between the metallic and polymeric ureteral stent groups. In terms of the cost, we assumed that all ureters underwent RUS with local anesthesia and that the median survival time was 2 years.

Conclusions
We compared the cost between metallic and polymeric ureteral stents at 2 and 2.5 years after insertion of an indwelling ureteral stent. To evaluate the workload of the medical staff, we used the NASA Task Load Index (NASA-TLX). 19,20 The NASA-TLX is widely regarded as the gold standard for measuring subjective workload.
It provides an overall workload score based on a weighted average of ratings on six subscales: Mental Demands, Physical Demands, Temporal Demands, Performance, Effort, and Frustration. We also compared the workload score between metallic and polymeric ureteral stent in a total of 11 urologists.

| Statistical analyses
Univariate and multivariate logistic regression analyses were per-   (Table 5).

| Patients' characteristics and outcomes
A Kaplan-Meier analysis and log-rank test indicated that there were no significant differences between the two groups in the overall survival (P = .673; Figure 1). It also indicated that there were no significant differences between the two groups in the rate of stent failure (P = .498; Figure 2).

| Complications analyses
The frequency of complications is summarized in  (Table 4).
A univariate analysis revealed that the age (<60 vs ≥60 years; P = .017) was associated with complications, whereas the gender, type of cancer, pre-stenting, and history of chemotherapy and radiotherapy were not associated with complications. A multivariate analysis revealed that no factors were associated with complications (Table 5).

| Cost analyses
The cost of placing metallic and polymeric ureteral stents for 2 years

| Workload analyses
We sent out questionnaires to 11 urologists experienced in replacement metallic ureteral stents. All urologists answered this questionnaire experienced metallic ureteral stenting more than five cases. The average workload score in six subscales was analyzed ( Figure 3). The mental demand and performance scores were higher for metallic ureteral stent, but there was no significant difference between metallic and polymeric ureteral stents. Several subsequent studies have reported that the mean follow-up duration ranged from 5 to 12 months, with no major complications. The patency rate ranged from 46% to 100%. 2,22 While studies of metallic ureteral stents have involved fewer patients than those of polymeric ureteral stents, the patency rate was higher. 15 The safety and efficacy of metallic ureteral stents has been recog- This study has several limitations as follows. The first one is that the number of urologist to answer NASA-TLX is small. On the contrary, in our institute, the procedure were standardized using the lecture by expert and all urologists experienced metallic ureteral stenting more than five cases. Further study is needed to confirm which subject was affected between polyurethane ureteral stenting and metallic ureteral stenting. The second one is this study could not reveal the differences of complications between young and elderly.

| D ISCUSS I ON
Younger age (<60) group showed significantly higher than elderly (≥60) group. In these patients, 5 of 11 (45.5%) were gynecological cancer. Thus, females with gynecological cancer showed irritation in higher percentage.

| CON CLUS ION
Metallic ureteral stents showed favorable ureteral stent patency and helped reduce the workload for urologists.

CO N FLI C T O F I NTE R E S T
We declare no conflicts of interest.

E TH I C S A PPROVA L A N D CO N S E NT TO PA RTI CI PATE
This study was approved by the ethics committee of Yokohama City University Medical Center. Approval number is B180900072.

DATA AVA I L A B I L I T Y S TAT E M E N T
Due to ethical restrictions, the raw data that were used in this study are available upon request from the corresponding author.