2.1

Study population

We included data on 1,002 adult (ages ≥ 21 years) patients who were members of one of three integrated health care systems who were diagnosed with bladder cancer between 01/01/2010–05/30/2015 and who underwent radical cystectomy with urinary diversion [ ]. The integrated health systems included three Kaiser Permanente (KP) regions—KP Northwest (Oregon and southwest Washington state), KP Northern California, and KP Southern California – serving a total of approximately 9.8 million members. For the current analysis, we included patients who received ileal conduit ( n = 821) or neobladder ( n = 181) UDs and excluded patients who received a continent pouch UD ( n = 30). The study received institutional review board approval from all 3 health systems.

2.2

Data sources

Data for this study were obtained from clinical and administrative data systems at the three participating sites, and included: demographic variables – age at cystectomy, sex, race, and Hispanic ethnicity; study site; health insurance type; clinical variables – year of cystectomy, UD type, Charlson-Deyo Comorbidity Index [ ], American Joint Committee on Cancer (AJCC) stage at cystectomy, presence of any complications in the year following cystectomy, vital status, robot-assisted surgery, and months since cystectomy. We extracted utilization data from hospital discharge abstracts; claims; hospital, emergency room, same-day surgical, and medical office ambulatory care encounters. Data were standardized across the participating sites according to specifications established by the Health Care System Research Network’s Virtual Data Warehouse [ ].

2.3

Medical care cost estimates

Medical care costs were calculated by applying cost coefficients to monthly counts of the following utilization categories: inpatient days, same-day surgeries, hospital ambulatory encounters, emergency room visits, and outpatient clinic visits. Outpatient visit counts were further divided into the following groups: primary care, oncology, nephrology, urology, cardiology, and other specialty visits. Cost coefficients were based on average cost per visit per utilization category, using a hybrid methodology from Medicare fee schedules (e.g., inpatient day, hospital ambulatory, same-day surgery) [ ] and administrative data from KP (i.e., medical care costs for services provided both in network and out of network. Cost coefficients used in the analysis are shown in Supplementary Table 1 . Monthly medical care costs per patient were estimated from the month of radical cystectomy (month 0) through the 11 months following cystectomy, then averaged across quarters: Quarter 1 (Q1) = month 0 through month 2; Quarter 2 (Q2)=month 3 through month 5; Quarter 3 (Q3) = month 6 through month 8; and Quarter 4 (Q4) = month 9 through month 11. Costs of the initial surgery were included as part of the first quarter cost estimates. Costs were adjusted for inflation using the Consumer Price Index for Medical Care in 2022 [ ].

2.4

Statistical analysis

We calculated descriptive statistics for patients with each UD type, including frequencies, means, proportions, and standard deviation (SD), for patient demographic and clinical characteristics [ ]. We present the mean and SDs for unadjusted monthly medical care utilization rates, by quarter and UD type, for the following service categories: inpatient stays and days, emergency department (ED) visits, primary care (PC) visits, and specialist visits.

To account for confounders, we developed a propensity score using logistic regression that included race, Hispanic ethnicity, health insurance type, sex, receipt of neoadjuvant therapy, body mass index and study site as predictors. The variables included in the propensity score were considered potential confounders based on prior research [ ]. To check the performance of the propensity score in achieving balance, we calculated standardized differences between the ileal conduit and neobladder patients before and after adjustment for the propensity score. The largest standardized difference prior to propensity score adjustment was .46 (for site 1) whereas after adjustment all values were near zero, with the largest difference being .015 for sex; well below the .10 cutoff proposed by Normand et al. [ ] and the 0.25 cutoff by Rubin [ ].

We used generalized linear models with a gamma distribution and log link [ ] to estimate mean monthly medical care costs per quarter, adjusting for UD type, age at cystectomy, Charlson-Deyo Comorbidity Index, presence of any complications, stage at cystectomy, year of cystectomy, robot-assisted surgery, death in quarter, and the propensity score. Adjustment variables were selected based on prior literature on medical costs of bladder cancer [ ]. Few studies having assessed medical care costs by UD type [ , ] Cost estimates and 95% confidence intervals (95% CI) for UD type, tumor stage at cystectomy, presence of any complications, surgical approach, and death in quarter were obtained from the multivariable model. In this complete-case study, SAS [version 9.1] and STATA [version 15] were used for all statistical analyses.

3.1

Patient demographics

Study population characteristics by UD type are presented in Table 1 . Patients who received a neobladder were more likely to be younger (age at cystectomy ≤ 64 years, 59% vs. 22%, P < 0.001), female (90% vs. 76%, P < 0.001), have a lower comorbidity burden (Charlson-Deyo Comorbidity Index ≤ 2, 48% vs. 27%, P < 0.001), have lower tumor stage (AJCC stage at cystectomy 0 or 1, 30% vs. 21%, P < 0.001), and have undergone robotic surgery (22% vs. 8%, P <0.001) than patients who received an ileal conduit. Patients who received a neobladder were less likely than those who received an ileal conduit to die within the first year of surgery (13% vs. 25%, P < 0.001).

Table 1

Study Population Characteristics

	Urinary Diversion Type
	Ileal Conduit		Neobladder
	( n = 821)		( n = 181)
	n	%	n	%
Age group at Cystectomy a
< 55 years	26	3.2	37	20.4
55–64 years	157	19.1	69	38.1
65–74 years	296	36.1	59	32.6
≥ 75 years	342	41.7	16	8.8
Sex a
Male	627	76.4	162	89.5
Female	194	23.6	19	10.5
Race
White	686	83.6	147	81.2
Non-White	135	16.4	34	18.8
Hispanic Ethnicity
Hispanic	79	9.6	20	11.1
Non-Hispanic	742	90.4	161	89.0
Charlson Comorbidity Index a
≤ 2	218	26.6	86	47.5
3	161	19.6	35	19.3
4	132	16.1	22	12.2
≥ 5	310	37.8	38	21.0
AJCC Stage at Cystectomy a
0 or I	171	20.8	55	30.4
II	194	23.6	64	35.4
III or IV	456	55.5	62	34.3
Body Mass Index (BMI)
Normal	249	30.3	57	31.5
Overweight	349	42.5	72	39.8
Obese	223	27.2	52	28.7
Surgical Approach a
Robotic	67	8.2	40	22.1
Open	754	91.8	141	77.9
Any complications in the year following cystectomy
Yes	624	76.0	150	82.9
No	197	24.0	31	18.1
Died within year after surgery a	202	24.6	23	12.7
Follow-up Time, months a
Mean (SD)	10.4 (3.1)		11.2 (2.3)
Median (IQR)	12.0 (8.3, 12.5)		12.0 (9.6,12.8)

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