Risk factors in the prediction of long‐term patency of Resonance metallic ureteric stent in malignant ureteric obstruction

Abstract Objectives Cancer is the second leading cause of death globally in 2018 with an estimated 9.6 million deaths. The costs of managing malignant ureteric obstruction (MUO) is a significant burden to any healthcare system. However, the management of MUO has long been a challenge for urologists. The standard options of percutaneous nephrostomy or polymer double J stents are fraught with problems. We report a large patient series with long‐term follow‐up in the use of Resonance metallic ureteric stents to relieve MUO, and identification of risk factors associated with stent failure. Patients and methods All patients with MUO who were arranged to have Resonance metallic ureteric stent insertion at two university hospitals were included in this cohort study, starting from June 2011 to July 2016. Data were retrieved retrospectively. The primary outcome was the total duration of stent patency before stent failure due to malignant disease progression. Stent failure was defined as ureteric obstruction identified on imaging (functional radioisotope scan or antegrade pyelogram), acute renal failure resolved by subsequent percutaneous nephrostomy, or any other cause requiring stent removal prematurely. Secondary outcomes were identification of factors associated with stent failure, grade III or above complication, and development of a risk‐adopted model to predict metallic ureteric stent patency rates in MUO patients. Median duration of functioning metallic ureteric stent was determined with Kaplan‐Meier survival curve. Results A total of 124 renal units in 95 patients with MUO were eligible for the study, with a median follow‐up period of 22.9 months. About 106 (85.5%) renal units had successful metallic stent insertion, of whom 41 (33.1%) renal units ultimately progressed to ureteric obstruction despite the metallic stents, and required subsequent insertion of nephrostomies. Median duration of functioning metallic ureteric stents was 25 months. Female gender (HR 3.0, 95% CI: 1.3‐7.2, P = .014) and suspicious bladder lesion (HR 2.9, 95% CI: 1.4‐6.2, P = .005) were independent risk factors for stent failure, respectively. Stratifying patients into low (0 risk factor), intermediate (1 risk factor), and high (2 risk factors) risk groups, we found that this could predict the duration of stent patency in MUO with the metallic stents. (Low risk: 30.3 months vs intermediate group: 17.8 months vs high risk: 4.9 months, P < .001). Conclusion Resonance metallic ureteral stents are able provide a median of 25 months of ureteric drainage in patients with MUO. Determining whether a patient has one or both risks factors (female gender and bladder lesion) will allow one to estimate the duration of metallic stent patency, which in turn may aid in determining cost‐effectiveness in individual patients.


| INTRODUC TI ON
Cancer is the second leading cause of death globally in 2018 with an estimated 9.6 million deaths. 1 The costs of managing malignant ureteric obstruction (MUO) is a significant burden to any healthcare system. 2  The Cook Resonance metallic ureteric stents were first introduced in 2006 with a nonmagnetic nickel-cobalt-chromium-molybdenum body in a spiral coil design. It has been demonstrated to be highly resistant to external compressive forces, being at least three to four times more robust than traditional polymer stents. 4,5 However, studies on the durability of Resonance metallic ureteric stents have been limited to small case series. This study aimed to identify risk factors associated with Resonance metallic ureteric stent failure due to malignant disease progression, and to propose a simple scoring system for the prediction of long-term patency of metallic stent in patients with MUO.

| PATIENTS AND ME THODS
All patients with unilateral or bilateral MUO were offered Resonance metallic stent insertion at two university teaching hospitals between June 2011 to July 2016, except for patients who were clinically frail or patients who had previous urinary diversion surgery. Patients who were arranged for insertion of Resonance metallic ureteric stents were retrospectively identified using an institutional electronic patient records database. Patients with ureteric obstruction due to benign causes were excluded from analysis in this study. Patient demographics, level of ureteric obstruction, nature of obstruction, previous history of irradiation, presence of intravesical tumor or localized cystitis, need for intraoperative ureteric dilation, presence of preoperative double J stents or nephrostomy tube, preoperative and postoperative serum creatinine, and duration of functioning metallic ureteric stents were recorded. All the follow-up appointments and imaging were arranged as necessary in the management of their cancer.
There were no fixed follow-up scheduled for this study besides the annual revision of Resonance metallic stents.

| Insertion of Resonance metallic ureteric stents and subsequent management
All Resonance metallic ureteric stents were inserted in a standardized retrograde fashion under both cystoscopic and fluoroscopic guidance. Retrograde pyelogram was first carried out in all patients to confirm level of obstruction. Ureteric length was measured was 25 months. Female gender (HR 3.0, 95% CI: 1.3-7.2, P = .014) and suspicious bladder lesion (HR 2.9, 95% CI: 1.4-6.2, P = .005) were independent risk factors for stent failure, respectively. Stratifying patients into low (0 risk factor), intermediate (1 risk factor), and high (2 risk factors) risk groups, we found that this could predict the duration of stent patency in MUO with the metallic stents. (

| Outcome measures
The primary outcome measure was the total duration of stent patency before stent failure due to malignant disease progression.

| Statistical analysis
Data were analyzed using SPSS v20. Median duration of functioning metallic ureteric stent was determined with Kaplan-Meier survival curve. Univariate and multivariate Cox regression analysis was used to identify risk factors. Fisher's exact test was used when analyzing other categorical variables. Ethics approval was obtained from the local institutional review board.     Others reported the one year patency rates of Resonance metallic stents in malignancy ureteric obstruction ranged from 60% to 91%. [15][16][17][18] However, determining when the metallic Resonance stent will fail due to disease progression is better represented by Kaplan-Meier survival since a significant portion of stents will be function- found that serum creatinine of ≥2 mg/dL (176.8 µmol/L), age ≥ 60, and non-lower gastrointestinal cancers were associated with shorter duration of functioning metallic stents. 13 24 Thus, we did not offer Resonance stents for this cohort of patients.

| CON CLUS ION
The Resonance metallic ureteric stents has a good median functioning duration of 25 months for patients with MUO. Female gender and suspicious lesions in the bladder were independent risk factors for stent failure. The proposed three-tier scoring system helps to predict long-term Resonance metallic stent patency rates, which in turn may aid in determining cost-effectiveness in individual patients.

D I SCLOS U R E
None of the authors have any conflict of interests to disclose.