Wuwei cohort and participants
Wuwei, a prefecture-level city located in the eastern region of the Hexi Corridor in Gansu Province, is considered an ideal high-incidence region site for conducting a population-based cohort study for gastric cancer [13]. According to the Wuwei Cohort, 25,000 native residents aged from 35 to 70 years were selected using a cluster sampling method. The final count for gastroscopies performed on these participants was 21,345, and the compliance rate to endoscopy was 85.4%. In addition to gastroscopy, 21,291 participants were tested for H. pylori with UBT, and 9,396 were tested for serum PGⅠ, PGⅡ and HPA using an automated biochemical analyzer (Fig. 1).
Almost 53.0% of the participants were H. pylori-positive as detected by 14C-UBT, 60.3% were H. pylori IgG positive, and 27.67% were PG-, positive. Individuals who tested positive for the H. pylori infection (including both true and false positive) would recommend receiving standard 14-day bismuth quadruple therapy (20 mg omeprazole, 1 g amoxicillin, 500 mg clarithromycin, twice daily), which was recommended by the Chinese H. pylori guidelines and the Maastricht V conference report. Through 21,345 cases of gastroscopic examinations, 167 GC cases were confirmed by pathological diagnosis, with 103 cases of early gastric cancer and 64 cases of advanced gastric cancer, indicating an overall gastric cancer detection rate of 0.8% and an early GC proportion of 61.7%. Additional details and baseline data of this cohort study are available in Ji et al. [13]. Data characteristics of multiple gastric cancer screening strategies are summarized in Supplementary Table S1. The Ethics Committee of The First Hospital of Lanzhou University approved this study (approval number: LDYYLL2012001).
Markov Model
The Markov model is a process that models random events that occur over time and has been increasingly applied to areas in health economic research in recent years, such as screening for disease, decision analysis of clinical interventions, pharmacoeconomic evaluation, and so on [14, 15]. The principle is to divide the natural course of the disease into several different health states (Markov state) and to stimulate the development of the disease according to the transition probability of each state in a certain period (Markov cycle). This information is combined with each state's health utility values and the public health resource consumption to estimate the outcome and the cost of disease progression through multiple iterations [16].
We synthesized information from regionally representative data sets on demographics, gastric cancer incidence, mortality, survival rate and the Wuwei Cohort database (Table 1). Using these data, we developed a Markov decision model using TreeAge Pro Healthcare 2020 (Tree Age Software, Williamstown, WA, USA) to inform long-term outcomes of 22 strategies with various screening methods, different screening intervals at different starting and stopping ages of gastric cancer, which was representative of the population of Northwest China, a region of high incidence. The natural history of disease progression was simulated based on Correa’s cascade [17] of gastric carcinogenesis of intestinal-type non-cardia gastric adenocarcinoma (NCGA), the primary histologic type of gastric cancer (Fig. 2). As a simulated individual ages, precancerous lesions (atrophy gastritis, intestinal metaplasia, or dysplasia) may develop. Preclinical cancer may either become symptomatic, be detected by screening, or progress to a more advanced preclinical cancerous stage. A healthy individual can transition to atrophy gastritis or remain stay in a normal state. Patients at state atrophy gastritis can progress to intestinal metaplasia, dysplasia, early gastric cancer (EGC) and advanced gastric cancer (AGC) in turn. Patients also can regress to less advanced precancerous lesions before dysplasia develops.
Model assumptions
To simplify the case study, several fundamental assumptions made in this research are: a) the healthy asymptomatic individuals with or without H. pylori infection were in perfect health, with the health-state utility of 1 [9]; b) a Markov process did not reverse the severe state of dysplasia [17, 18]; c) the ABC method plus endoscopy screening was allocated to four Groups (A-D) with different risks of gastric cancer ([19] and the periodic endoscopic examination should be taken for patients in Group B, C, and D at the interval of 3, 2, and 1 year, respectively, except for Group A due to their low-level risk of developing gastric cancer [20]; d) all suspected cases proceeded to biopsy, and all diagnosed cases received treatment; e) all individuals with primary and secondary prevention strategies were undergo screening; f) all individuals could die from causes other than gastric cancer during disease progression, but only patients at state AGC could die from gastric cancer.
Modelling strategies
As gastric cancer is commonly seen in an old population, we used an annual endoscopic screening frequency from 40 to 75 years as the baseline. We also explored 20 other scenarios compared with no screening, in addition to seven strategies with endoscopic screening varying starting ages (40 and 50 years), screening intervals (1, 2, and 3 years) and stopping periods (75 and 80 years). We also evaluated three strategies with H. pylori screen-and-treat varying starting ages (20, 30, and 40 years) and with the same stopping ages of 80 years; seven techniques with the serum PG method varying starting ages (40 and 50 years), screening intervals (1, 2, and 3 years) and stopping periods (75 and 80 years); and four strategies with the serum ABC method varying starting ages (40 and 50 years) and stopping ages (75 and 80 years).
Input parameters
The epidemiologic parameters, state-transition probabilities, health-state utility, and treatment cost used in the model are listed in Table 1. We obtained the age-specific gastric cancer incidence from Chinese literature about the 2012 cancer incidence analysis of Wuwei Municipality, Gansu Province, China [21]. We employed H. pylori prevalence according to an all-age population-based cross-sectional study in the Wuwei region [22]. The initial distributions of the cost-effectiveness analysis in different Markov states were determined from the Wuwei Cohort epidemiologic database (Supplementary Table S2). We calculated age-specific mortalities from other causes by subtracting age-specific GC mortality rates from the corresponding age-specific all-cause mortality rates of rural residents in 2019 from the China Health Statistics Yearbook 2020 [23].
Table 1
Key input model parameters included in our study
Parameters
|
Baseline
|
Range
|
Distribution
|
References
|
Clinical and epidemiologic variables
|
|
|
|
|
Age at screening initiation (years old) (PG/ABC/Endoscopy)
|
40, 50
|
40–70
|
Uniform
|
Assumption
|
Age at screening initiation (years old)
(H. pylori screening)
|
20, 30, 40
|
20–60
|
Uniform
|
Assumption
|
Age-specific all-cause mortality
(per 100,000)
|
37.72-7668.76a
|
Fixed
|
Fixed
|
[23]
|
Age-specific incidence of gastric cancer
(per 100,000)
|
6.44-616.30a
|
Fixed
|
Fixed
|
[21]
|
Age-specific mortality due to gastric cancer
(per 100,000)
|
0.29-175.33a
|
Fixed
|
Fixed
|
[23]
|
Age-specific prevalence rates of H. pylori (%)
|
|
|
|
|
20-
|
36.4
|
Fixed
|
Fixed
|
[22]
|
30-
|
50.3
|
Fixed
|
Fixed
|
[22]
|
40-
|
56.3
|
Fixed
|
Fixed
|
[22]
|
Annual H. pylori infection rate (%)
|
1
|
0.25-4
|
Beta
|
[41]
|
Annual H. pylori reinfection rate after eradicated (%)
|
1
|
0.6–1.4
|
Beta
|
([38]
|
Eradication rate of bismuth quadruple therapy (%)
|
85.51
|
74.71–96.41
|
Beta
|
([44]
|
Relative risk of gastric cancer development with H pylori infection
|
2.36
|
1.98–2.81
|
Lognormal
|
[45]
|
Relative risk of gastric cancer development with H pylori eradication
|
0.66
|
0.46–0.95
|
Lognormal
|
[46]
|
Serum pepsinogen positive rate (%)
|
27.67
|
Fixed
|
Fixed
|
[47]
|
Transition probabilities of disease progression
|
Normal to atrophy gastritis
|
0.017
|
Fixed
|
Fixed
|
[25, 48]
|
Atrophy gastritis to intestinal metaplasia
|
0.079
|
Fixed
|
Fixed
|
([25, 48]
|
Intestinal metaplasia to dysplasia
|
0.040
|
Fixed
|
Fixed
|
[48]
|
Dysplasia to early gastric cancer
|
0.380
|
Fixed
|
Fixed
|
[48]
|
Early gastric cancer to advanced gastric cancer
|
0.429
|
Fixed
|
Fixed
|
[25]
|
Advanced gastric cancer to death
|
0.214
|
Fixed
|
Fixed
|
[49]
|
Transition probabilities of disease regression
|
Atrophy gastritis to normal
|
0.016
|
Fixed
|
Fixed
|
[48]
|
Intestinal metaplasia to atrophy gastritis
|
0.037
|
Fixed
|
Fixed
|
[48]
|
Quality of life utility
|
|
|
|
|
Health
|
1
|
Fixed
|
Fixed
|
Assumption
|
Gastric precancerous lesion (AG, IM, dysplasia)
|
0.90
|
0.77–0.90
|
Beta
|
[50] Wuwei Cohort
|
Early gastric cancer
|
0.87
|
0.63–0.92
|
Beta
|
[50] Wuwei Cohort
|
Advanced gastric cancer
|
0.83
|
0.55–0.83
|
Beta
|
[50] Wuwei Cohort
|
Death
|
0
|
Fixed
|
Fixed
|
Assumption
|
Costs (US dollars)
|
|
|
|
|
Screening cost
|
|
|
|
|
Endoscopic screening with biopsy
|
100
|
90–160
|
Gamma
|
[24] Wuwei Cohort
|
H pylori screening test (UBT)
|
15
|
12.04–40.14
|
Gamma
|
[26] Wuwei Cohort
|
PG test
|
15
|
12–40
|
Gamma
|
[26]) Wuwei Cohort
|
PG and HPA test
|
30
|
14–42
|
Gamma
|
[24] Wuwei Cohort
|
Treatment cost
|
|
|
|
|
H pylori eradication treatment
|
28.27
|
9.78–59.23
|
Gamma
|
[9]
|
Endoscopic submucosal dissection
|
3,700
|
1400-23,570
|
Gamma
|
[26, 51]
|
Surgery
|
7,692
|
4069-18,578
|
Gamma
|
[52]
|
Chemotherapy treatment for advanced gastric cancer totally
|
5,256
|
3169-9,728
|
Gamma
|
[52]
|
Palliative care for annual cost of illness
|
4,331
|
2587-10,770
|
Gamma
|
[52]
|
Discount rate (%)
|
3
|
|
|
[29]
|
Notes: a Values were age-specific from age of 20 to age of 80+; PG, pepsinogen; ABC, a combination of serum PG and H. pylori IgG antibody (HPA); H. pylori, Helicobacter pylori; the cutoff of ABC method, PG I ≤ 60 ng/ml, and PG I/II ratio of ≤ 3.0; AG, atrophy gastritis; IM, intestinal metaplasia.
Transition Probabilities
The transition probability (p) of an event occurring over a specific time interval (t) was calculated using an incidence rate (r) (p = 1-exp(-rt)) [24]. Regarding the progression rates between different Markov states and the relative death risk of AGC, we obtained data from the studies whose data were derived from a community-based screening program for gastric cancer in the Matzu region of Taiwan also has a very high incidence rate of GC [25, 26] and assumed that the parameters applied to Northwest China.
Costs
Cost data directly or indirectly related to gastric cancer screening were collected from the project audit information, the internal accounts of hospital screening units, and published studies. The cost data of the other expenditures for different stage gastric cancer treatments were obtained from the hospital information system of local hospitals.
Utilities
The generic health status and health-related quality of life (HRQoL) were expressed by health utility weights (HUWs). HUWs are valued between 0 and 1 according to how individuals perceive or her health status. Quality-adjusted life-years (QALY), which reflects both length of life and health-related quality of life, was calculated as the product of the utility score of a particular state of health, defined as a dimensionless number between 1 (perfect health) and 0 (death), and the number of years lived [27]. We identified the utility scores for patients from a cross-sectional study also carried out in Wuwei region as part of the screening program, in which before patients underwent upper endoscopy (n = 1908) using the EQ-5D-5L quality of life questionnaire. The main patient characteristics and utilities according to stages of the gastric cancer cascade are summarized in Supplementary Table S3. To calculate QALYs, we assumed that healthy asymptomatic individuals were in perfect health, with a health-state utility of 1.
Other parameters
Willingness To Pay (WTP)
In a developing country, the maximum price of one year of a healthy life is around threefold the annual earning per capital [28]. The gross domestic product (GDP) per capita in Gansu, China in 2018 was US$ 5,000. The maximum WTP for a QALY gained in this study of about US 15,000 was estimated based on the above approach.
Cost-effectiveness analysis
In agreement with the China Guidelines for Pharmacoeconomic Evaluations, we discounted all costs and clinical consequences by 3% annually [29]. For the cost-effectiveness analysis, all results were scaled to 10 million individuals. To evaluate the relative performance of each strategy, we estimated the lifetime costs of screening and its effects in terms of QALY. We calculated the incremental cost-effectiveness ratios (ICERs), defined as the additional cost of a specific strategy divided by its additional clinical benefit, compared with no screening strategy, and expressed as cost per QALY. A strategy was dominated if it was more costly but yielded fewer QALYs than its adjacent strategy or had a higher ICER than a more effective strategy. All costs are reported in 2018 US dollars (1 U.S.$=6.7 RMB). An ICER of less than US$ 15,000/QALY is therefore an indication that the screening strategy for high-risk Chinese, compared with no screening, is cost-effective.
Sensitivity analyses
We conducted one-way and probabilistic sensitivity analyses to explore the effect of parameter uncertainty [30–32]. In the one-way sensitivity analyses, we used the minimum and maximum estimates for all key parameters, testing the influence of extreme variations in each parameter on the overall results. We varied each parameter individually to assess its impact on overall results. Probabilistic sensitivity analyses were done with a Monte Carlo simulation to investigate the effect of parameter uncertainty on the cost-effectiveness results. The input variables were specified as distributions: costs have a gamma distribution, and utility values follow lognormal distributions, as suggested in the literature [33]. we performed 1000 second-order Monte Carlo simulations to explore the influence of uncertainty on those key parameters. In addition, we generated cost-effectiveness acceptability curves for all competing strategies. The definition of cost-effectiveness acceptability curves was the probability that a strategy was most cost-effective among all alternatives given a wide range of WTP thresholds.