Statin use and its association with decreased risk of esophageal squamous cell carcinoma in betel nut chewers

Abstract Background Betel nut chewing involves the chewing of areca nuts or betel quid (areca nuts wrapped in betel leaves), which is associated with an increased risk of esophageal squamous cell carcinoma (ESCC). Statins have anticancer properties. We investigated the association between statin use and ESCC risk in betel nut chewers. Methods The study included 105 387 betel nut chewers matched statin users and nonusers. Statin use was defined as the use of ≥28 cumulative defined daily doses (cDDDs) of statin. The primary outcome was incidence of ESCC. Results The incidence rate of ESCC was significantly lower in statin users than in nonusers (2.03 vs. 3.02 per 100 000 person‐years). Statin users had a lower incidence rate ratio of 0.66 for ESCC (95% confidence interval [CI]: 0.43–0.85) relative to nonusers. After potential confounders were adjusted for, statin use was determined to be associated with a reduced risk of ESCC (adjusted hazard ratio [aHR], 0.68; 95% CI: 0.51–0.91). A dose–response relationship was observed between statin use and ESCC risk; the aHRs for statin use at 28–182 cDDDs, 183–488 cDDDs, 489–1043 cDDDs, and > 1043 cDDDs were 0.92, 0.89, 0.66, and 0.64, respectively. Conclusion Statin use was revealed to be associated with a reduced risk of ESCC in betel nut chewers.


INTRODUCTION
Betel nut chewing is a widespread practice in Taiwan and was first introduced to the majority Han population by the native indigenous peoples of Taiwan. 1 Estimates indicate that more than NT$100 billion is spent annually on this product, which is colloquially known as "Taiwanese chewing gum." 2 The high consumption of betel nut, cigarettes, and alcohol in Taiwan has contributed to its high incidence of head and neck cancer. 3 The prevalence of betel nut chewing in Taiwan (lifetime prevalence of 10%) 4 has caused it to become a major public health concern. Betel nut chewing involves the chewing of areca nuts or betel quid (areca nuts wrapped in betel leaves), which is associated with an increased risk of several types of cancer, 5 including esophageal squamous cell carcinoma (ESCC). 6,7 The exact mechanism through which betel nut chewing increases the risk of ESCC is not fully understood, but it is speculated to involve the release of copper, which leads to collagen synthesis by fibroblasts. 8 This phenomenon is also associated with a younger age of diagnosis, poor chemotherapy response, poor radiotherapy response, and shorter overall survival in patients with ESCC. 9 Given the high prevalence of betel nut chewing in the Taiwanese population, the habit is a particularly relevant risk factor for ESCC in Taiwan. The overall survival rate for ESCC is poor both globally and in Taiwan. [10][11][12][13] The mean age of diagnosis of ESCC in Taiwan is approximately 50 years old, [10][11][12][13] and patients with ESCC are often economically active individuals and the main breadwinners in their families. Discovering effective protective medications against ESCC is a valuable and crucial goal in the context of a high population of betel nut chewers.
Statins are a class of drugs that are commonly used to reduce cholesterol levels and the risk of cardiovascular disease. 14 Studies have indicated that statins have anticancer properties. 15,16 Several studies have reported an association between statin use and a reduced risk of various types of cancer, including esophageal, gastric, colorectal, liver, and lung cancer. 17 Although the mechanisms underlying the anticancer effects of statins remain unclear, several explanations have been proposed. The first explanation is that statins inhibit cancer cell growth and spread by reducing proteolysis and having antiproliferative, antiangiogenic, proapoptotic, and immunomodulatory effects. 18,19 The second explanation is that statins modulate fibrosis progression, which is an underlying mechanism that contributes to the development of cancer. 20 Studies have also reported that statins have strong antifibrosis, anti-inflammatory, and immunomodulatory effects. 21 Statins reduce the activity of inflammatory signaling pathways, 22,23 which is associated with an increased cancer risk. In addition, several studies have indicated that statin use is associated with a reduced esophageal cancer risk, especially in patients with Barrett's esophagus. [24][25][26] We conducted a long-term, head-to-head comparative national cohort study by employing propensity score matching (PSM) to understand the association between statin use and the risk of ESCC in betel nut chewers who are at high risk of ESCC and have poor overall survival, particularly in relation to their betel nut chewing habits. Additionally, we verified whether a dose-response relationship was present. The present study is the first to investigate the relationship between statin use and ESCC risk in betel nut chewers, and it provides valuable insights that can guide future research in this area.

Study population
We conducted a population-based cohort study using data from the Taiwan National Health Insurance (NHI) Research Database (NHIRD) for the period from 2008 to 2018. The NHIRD stores comprehensive medical claims data on all NHI beneficiaries, including their diagnoses, procedures, drug prescriptions, demographics, and enrollment profiles, all of which are encrypted using unique patient identifiers. [27][28][29][30][31][32] Because the NHIRD is linked to the death registry, the vital status and cause of death of each included patient could be determined. The NHIRD is a valuable resource for population-based research because it covers the entire NHI-insured population of Taiwan, which represents more than 99% of the Taiwanese population. [28][29][30][31][32] In Taiwan, the Health Promotion Administration of the Ministry of Health and Welfare initiated an oral cancer screening program in 2004. 33 The population determined to be at the highest risk of developing oral cancer was determined to be that with a betel nut chewing habit, and patients with this habit were identified through a link between the National Oral Cancer Screening database and the NHIRD. Therefore, we included patients who were betel nut chewers and enrolled in the linked NHIRD and National Oral Cancer Screening database.
Our study included patients who were betel nut chewers, aged ≥20 years, and enrolled in the NHIRD and the National Oral Cancer Screening database; patients with missing age data were excluded. Statin use was defined as the use of ≥28 cumulative defined daily doses (cDDDs) of statin. The index date was the date on which a patient's statin use reached 28 cDDDs. The observation period for each patient began on the index date and continued until the patient was diagnosed with ESCC or until the end of the study period (December 31, 2021). Patients who died during the observation period were excluded to ensure that no competing risk of mortality was present between the case and control groups. The patients who were prescribed ≥28 cDDDs and <28 cDDDs of statin during the follow-up period formed the case group (statin users) and the control group (statin nonusers), respectively. The follow-up duration was defined as 1 year after the date of initial statin use or cohort entry. The present study is the first to investigate the association between statin use and ESCC risk, and it provides valuable information to clarify the risk of ESCC in the general population.
Patients were excluded if (1) they were given a diagnosis of ESCC within 1 year of the index date, (2) they had T A B L E 1 Baseline characteristics of statin users and nonusers among betel nut chewing patients after propensity score matching. missing data pertaining to their sex or age or were aged <20 years, (3) they had a follow-up duration of <1 year, or (4) they were given a diagnosis of any other type of cancer within 1 year of the cohort entry date (this criterion prevented ESCC-related metastases from influencing the results). These criteria were implemented to ensure that our results would accurately reflect the association between statin use and ESCC risk.
The study protocols were reviewed and approved by the Institutional Review Board of Tzu-Chi Medical Foundation (IRB109-015-B).

Study covariates
To control for potential confounding factors, we included several covariates in our analysis. The study participants were divided into four age groups (20-50, 51-60, 61-70, and ≥71 years) on the basis of their age on the index date. The index date for a statin user was defined as the date on which their statin use reached 28 cDDDs. For the matched statin nonusers, we used the variable data collected on the index date. To prevent repeated adjustments in our multivariate analysis, we excluded repeated comorbidities from our Charlson Comorbidity Index (CCI) calculations. We identified comorbidity onset within 1 year of the index date by using the International Classification of Diseases codes from either the main inpatient diagnosis or those from ≥2 outpatient visits within 1 year. These codes were from either the Ninth Revision, Clinical Modification (ICD-9-CM) or the Tenth Revision, Clinical Modification (ICD-10-CM).

Statin exposure
Statin use was defined as the use of ≥28 cDDDs of a statin. 29,34 Data on the drug type, dosage, administration route, prescription date, and total number of pills dispensed by a pharmacy were collected. Because statins could have been used in nonconsecutive years during the study period and the patients could have changed their drug use patterns over time, we treated statin use as a time-varying covariate in the Cox model. 35 The cumulative dose of statins was calculated by multiplying the number of pills dispensed for a prescribed dose and dividing the result by the recorded days' supply. The defined daily dose (DDD) of statins, as established by the World Health Organization, was used to express dosage. DDD is the average maintenance dose per day for a drug that is used for its main indication in adults, and cDDDs were calculated as the sum of the DDDs. Statin nonuse was defined as the absence of statin use or statin use amounting to <28 cDDDs (excluding occasional statin use), whereas statin use was defined as statin use amounting to ≥28 cDDDs. The included patients were divided into four subgroups on the basis of cDDD quartiles (Tables 1 and 3).

PSM and covariates
We used a time-varying Cox proportional hazards model to analyze the relationship between statin use and the onset of ESCC after controlling for potential confounders. To minimize the effect of confounding factors during the comparison of the ESCC risk of statin users and nonusers, we matched the patients on the basis of their propensity scores. The variables used for matching were age, sex, income level, urbanization level, cigarette smoking habit, alcohol-related diseases, comorbidities (diabetes, hypertension, chronic obstructive pulmonary disease, gastroesophageal reflux disease, Barrett's esophagus, obesity, achalasia, tylosis [Howel-Evans syndrome], Plummer-Vinson syndrome), medication use (aspirin, metformin, and proton pump inhibitors [PPIs]), and CCI score. Comorbidities were identified using In the present study, continuous variables are presented as means with standard deviations or medians with first and third quartiles. To minimize the differences between the patient groups, we employed the greedy method as a matching technique; specifically, PSM was conducted with a caliper width of 0.2 to match the patients at a ratio of 1:1. 36 This method involves selecting controls with identical background covariates that must be controlled for.

Primary endpoints
The primary outcome of this study was the occurrence of ESCC, which was confirmed by checking the certification records in the Registry for Catastrophic Illness Patients. 37 T A B L E 2 Time-varying Cox regression model of association of comorbidities and concurrent medications with esophageal squamous cell carcinoma risk in patients with betel nut chewing habits.

Statistical analysis
We collected information on patient characteristics, namely the included patients' age, sex, comorbidities, and statin dosage. Age was divided into 10-year intervals, and the baseline characteristics of statin users and nonusers were compared by performing chi-square tests for categorical variables, t tests for continuous variables, and Wilcoxon rank-sum tests for median values. The cohort entry date was set as the baseline. To assess the association between statin use and risk of ESCC, we calculated incidence rates (IRs) and incidence rate ratios (IRRs) and estimated adjusted hazard ratios (aHRs) with 95% confidence intervals (CIs) by employing Cox regression models and adjusting for age, sex, income level, urbanization level, cigarette smoking habit, alcohol-related diseases, comorbidities, medication use, and CCI score. The cumulative incidence of ESCC of the stain users and nonusers was estimated using the Kaplan-Meier method and compared using the log-rank test. All statistical analyses were performed using SAS for Windows (version 9.4; SAS Institute, Cary, NC, USA), and a two-sided p-value of <0.05 was regarded as statistically significant.

Baseline characteristics of study population
We analyzed the data of 210 774 individuals who were enrolled (in the aforementioned databases) between 2008 and 2018. The final follow-up date was December 31, 2020. To compare the data of the statin user and statin nonuser groups, we performed individual 1:1 matching, and each group comprised 105 387 patients. The age distribution of the two groups was similar (Table 1). Our PSM results revealed that the statin user and statin nonuser groups were comparable with respect to the variables of sex, income level, urbanization level, cigarette smoking habit, alcohol-related diseases, comorbidities, medication use, and CCI score. Table 2 presents the association of ESCC risk with concurrent medications and comorbidities in our study cohort. The risk of ESCC increased with age (patients aged 20-50 years were the reference group). Men had a higher risk of ESCC relative to women (aHR, 2.78; 95% CI: 2.23-3.46). Cigarette smokers had a higher risk of ESCC relative to nonsmokers (aHR, 1.21; 95% CI: 1.12-1.59), and patients with alcohol-related diseases had a higher risk of ESCC relative to those without such diseases (aHR: 6.42; 95% CI: 4.34-9.47). Table 3 presents the relationship between statin use and ESCC development in our cohort. The incidence rate of ESCC was significantly lower in statin users than in nonusers (2.03 vs. 3.02 per 100 000 person-years). Statin users had a lower incidence rate ratio of 0.66 for ESCC (95% CI: 0.43-0.85) relative to nonusers. After adjustments were made for age, sex, income level, urbanization level, cigarette smoking habit, alcohol-related diseases, comorbidities, medication use, and CCI score, the risk of ESCC was significantly lower among statin users than among nonusers (aHR, 0.68; 95% CI: 0.51-0.91).

IRs, IRRs, and aHRs for ESCC among statin users and nonusers
We also observed a dose-response relationship between statin use and ESCC risk, compared with statin nonuse T A B L E 3 Risk of esophageal squamous cell carcinoma in patients with betel nut chewing habits: estimated incidence rate ratios and adjusted hazard ratios. (<28 cDDDs), the aHRs for statin use at 28-182 cDDDs, 183-488 cDDDs, 489-1043 cDDDs, and >1043 cDDDs were 0.92, 0.89, 0.66, and 0.64, respectively. The p-value for the dose-response relationship trend was <0.001. The Kaplan-Meier analysis revealed that the ESCC risk was higher in statin users than in statin nonusers (Figure 1; log-rank test, p = 0.001). A similar trend was observed after the patients were stratified by statin cDDD (Figure 2; log-rank test, p = 0.001).

DISCUSSION
The chewing of areca nuts or betel quid (a mixture of areca nuts wrapped in betel leaves) is a widespread habit in numerous regions of Asia, and it is strongly implicated in the development of ESCC. 6,7 The mechanism underlying the association of areca nut chewing with ESCC may involve the release of copper, which induces collagen synthesis by fibroblasts. 8 Several studies have demonstrated that areca nut chewing is not only significantly and independently associated with an increased risk of ESCC 38 but also associated with a younger age of diagnosis, poor chemotherapy response, poor radiotherapy response, and a shorter overall survival in patients with ESCC. 9 Therefore, for regions with a high prevalence of betel nut chewing (e.g., Taiwan), 4,39 the safety and long-term effects of medications that provide protection against ESCC are crucial topics that must be investigated. Few studies have reported on the IR, IRR, and aHR of ESCC among betel nut chewers. Our study is the first to report on the IR, IRR, and aHR of ESCC among a population of betel nut chewers and estimate the other risk factors of ESCC in this population. Our results reveal that old age (>50 years), being male, smoking, and having alcoholrelated diseases are independent risk factors for ESCC in betel nut chewers. Additionally, this is the first study to report that statin use has an independent protective effect against ESCC in patients with betel nut chewing habits (Tables 2 and 3 and Figure 1) and that statin use reduces the risk of ESCC incidence (i.e., dose-response relationship; Table 3 and Figure 2). The mechanism through which statins reduce the risk of ESCC in a population with betel nut chewing habits remains unclear. Studies have suggested that statins inhibit cancer cell growth and spread, reduce proteolysis, and produces various effects (i.e., antiproliferative, antiangiogenic, proapoptotic, and immunomodulatory effects) through both statin-dependent and independent pathways. [40][41][42][43][44][45][46][47] Because the underlying mechanism of ESCC may involve collagen synthesis by fibroblasts due to betel nut chewing, 8 statins may modulate fibrosis progression through pathways other than inflammation. 48 This phenomenon may contribute to the reduction of ESCC risk. [41][42][43][44][45][46][47][48] Despite the diverse mechanisms of statins, the specific mechanisms that contribute to the reduction of ESCC risk in betel nut chewers remains unclear. Our study is the first long-term cohort study to indicate that statins are associated with a reduced ESCC risk in patients with betel nut chewing habits. However, it also highlights that the related mechanism is still unclear.
Studies have reported that statins provide protective effects against various types of esophageal cancer (e.g., adenocarcinoma). However, none have specifically focused on patients with betel nut chewing habits or on ESCC. [24][25][26] We verified the association of statin use with reduced ESCC risk in patients with betel nut chewing habits. This is a major finding because patients with betel nut chewing habits have a high risk of developing ESCC and other head and neck cancers. In future studies, we will further investigate the association between statin use and the risk of head and neck cancer in patients with betel nut chewing habits.
Our study reveals that several factors are associated with an increased risk of ESCC in betel nut chewers, namely older age (>50 years), male sex, cigarette smoking, and having alcohol-related diseases ( Table 2). These results are consistent with those of other studies on the risk factors for ESCC. [49][50][51][52] Our study verified that the risk factors for ESCC in betel nut chewers are similar to those reported in other studies. Therefore, in addition to statin use, quitting betel nut chewing, smoking, and alcohol are key factors that can reduce ESCC incidence.
The present study has several strengths, namely its use of a large sample size of betel nut chewers and a validation cohort, its long-term follow-up time, and its examination of the homogenous covariates between cases and controls after PSM and the long-term verification of medication data. However, several limitations must also be considered. First, although the National Health Insurance Administration routinely reviews patient charts to ensure the quality of the claims submitted by medical institutions, data miscoding or misclassification can still occur. Second, several unmeasured confounders related to ESCC (e.g., body mass index) were not included in our database. Third, we could not contact patients directly to confirm their statin use because their data were anonymized; thus, the nonadherence of patients to their prescribed medication regimen was unaccounted for. Our study reveals that statin use amounting to ≥28 cDDDs is a protective factor for ESCC. Specifically, we discovered that the patients who were prescribed statin at a dosage of ≥28 cDDDs had a significantly reduced risk of ESCC with a dose-response relationship. This finding indicates that using statin at a higher cDDD provides a greater protective effect against ESCC in patients with betel nut chewing habits. To verify these findings and further clarify the optimal safety dosage and duration of statin use for reducing the risk of ESCC, a large-scale randomized controlled trial must be conducted to compare carefully selected patients who are statin users or nonusers. Finally, the laboratory and clinical data used in the present study were not readily accessible through an administrative database.
In conclusion, our study revealed that statin use amounting to ≥28 cDDDs is a protective factor for ESCC and that patients who were prescribed statin at a dosage of ≥28 cDDDs had a significantly reduced risk of ESCC with a dose-response relationship. This finding indicates that using statin at a higher cDDD provides a greater protective effect against ESCC in patients with betel nut chewing habits.

DATA AVAILABILITY STATEMENT
The data sets supporting the study conclusions are included in the manuscript. We used data from the National Health Insurance Research Database and Taiwan Cancer Registry database. The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. The data used in this study cannot be made available in the manuscript, the supplemental files, or in a public repository due to the Personal Information Protection Act executed by Taiwan's government, starting in 2012. Requests for data can be sent as a formal proposal to obtain approval from the ethics review committee of the appropriate governmental department in Taiwan. Specifically, links regarding contact information for which data requests may be sent to are as follows: http://nhird.nhri.org.tw/en/Data_Subsets. html#S3 and http://nhis.nhri.org.tw/point.html. Informed consent was waived because the data sets are covered under the Personal Information Protection Act. Szu-Yuan Wu, MD, PhD had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.