1. Introduction
Statins are 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors that competitively block the active sites of lipid-lowering enzymes [
1]. The main therapeutic effect is inhibition of cholesterol biosynthesis. However, other diverse actions called “pleiotropy” were reported, including improvement of cardiovascular function [
2], anti-inflammatory effects [
3], and anti-fibrotic effects [
4,
5].
Some studies have indicated that statins exert anticancer effects by inducing apoptosis and inhibiting tumor cell growth and angiogenesis [
6,
7,
8]. Recent research suggests antitumor effects of statin [
9,
10,
11,
12] and its synergistic potency in chemo-resistant lung cancer populations [
13,
14,
15,
16].
Clinically, statin is associated with reduced all-cause mortality in interstitial lung disease and idiopathic pulmonary fibrosis (IPF) [
17,
18]. Also, statin attenuates decline in lung function in the elderly [
19]. Lung cancer is a common complication of IPF [
20,
21], with an incidence of approximately 22.9 per 10,000 person-years, which is approximately five times that in the general population. Kim et al. published a study showing that IPF patients with lung cancer had poor 5-year survival rates compared to non-IPF patients (14.5% vs. 30.1%;
p < 0.001) [
22]. Moreover, there was higher tendency of treatment-related adverse events [
23] such as postoperative clinical deterioration, acute exacerbation (AE), and radiation pneumonitis [
24,
25,
26] among IPF patients with lung cancer. Therefore, the importance of lung cancer prevention in IPF patients is very high.
To date, few studies have examined the role of statins in the risk of lung cancer development among IPF patients in large-scale cohorts. We analyzed the database of the National Health Insurance Service (NHIS) in Republic of Korea to further investigate the clinical impacts of consecutive statin use on lung cancer development and OS in IPF patients.
3. Results
The final analysis included 9,182 individuals diagnosed with IPF, of which 3,372 (36.7%) were statin users. The baseline characteristics of study patients are listed in
Table 1. The age at first diagnosis of IPF was younger in the statin user group (67.2 ± 11.2 vs. 64.0 ± 10.2,
p < 0.001). The proportion of males was higher in the statin non-user group (67.1% vs. 59.4%,
p < 0.001). Mean body mass index (BMI) (23.0 ± 3.2 vs. 24.0 ± 3.1,
p < 0.001), total cholesterol (184.2 ± 34.8 vs. 199.7 ± 42.6,
p < 0.0001), and systolic (125.2 ± 17.1 vs. 126.6 ± 16.8,
p < 0.0001) and diastolic blood pressure (76.3 ± 10.6 vs. 77.3 ± 10.8,
p < 0.0001) were higher in the statin user group. Smoking history as never, ex-, or current was not statistically different between statin users and statin non-users. However, the statin non-user group showed a higher smoking amount than the statin user group (38.1% vs. 25.7% for less than a half pack, 14.3% vs. 23.3% for a pack to less than two packs,
p < 0.001). In terms of drinking habits, the proportion of daily drinking (6.2% vs. 4.6%,
p = 0.004) was higher in the statin non-user group, but the amount consumed at a time (50.1% vs. 43% for one to two drinks; 7.2% vs. 12.7% for five to six drinks; 5.7% vs. 7.3% for seven to nine drinks;
p = 0.001) was lower. Interestingly, the frequency of no physical activity was higher (63.9% vs. 57.5%,
p < 0.0001) and the mean frequency of vigorous (0.8 ± 1.7 vs. 0.9 ± 1.8,
p = 0.022) and moderate (1.0 ± 1.9 vs. 1.2 ± 2.0,
p = 0.036) physical activity per week were lower in the statin non-user group. The proportion of comorbidities of hypertension (14.7% vs. 18.7,
p < 0.0001) and heart disease (3.0% vs. 4.2%,
p = 0.026) was higher in the statin user group, but that of cerebrovascular diseases (1.9% vs. 1.0%,
p = 0.013) was higher in the statin non-user group.
The clinical outcomes of this study are shown in
Table 2. Among 9,182 IPF patients analyzed during the study period, 850 were diagnosed as lung cancer. The incidence of lung cancer was similar in the statin user group and statin non-user group (9.2% vs. 9.4%,
p = 0.803) during the study period. However, the duration from the date diagnosed with IPF to the development of lung cancer was significantly longer in the statin group (2,194.6 ± 1601.4 vs. 3,361.0 ± 1331.2,
p < 0.001). Comparing the mortality rate between the statin user and non-user groups, OS was longer in the statin users (2413.9 ± 1778.7 vs. 3,741.8 ± 1443.1 days, Log rank
p < 0.0001) and total number of deaths was significantly lower in (66.9% vs, 41.6%, hazard ratio [HR] 0.41, 95% CI 0.39–0.44, Log rank
p < 0.0001). We obtained cumulative lung cancer incidence curves of stain users and statin non-users based on Kaplan-Meier plot analysis (
Figure 1).
In multivariate analysis using a Cox regression model for lung cancer development in IPF patients, higher statin compliance (adjusted HR [aHR] 0.66, 95% CI 0.48–0.90,
p < 0.001), statin use (aHR 0.63, 95% CI 0.53–0.76,
p < 0.001), and female sex (aHR 0.43, 95% CI 0.33–0.56,
p < 0.001) were independently associated with reduced lung cancer development in IPF patients. In contrast, the risk of cancer development increased in the group of patients diagnosed with IPF at an older age (aHR 1.05, 95% CI 1.04–1.06,
p < 0.001) and with smoking (aHR 1.55, 95% CI 1.39–1.72,
p < 0.001).
Table 3.
Cox proportional hazard regression analysis of the clinical variables affecting lung cancer development in IPF patients.
Table 3.
Cox proportional hazard regression analysis of the clinical variables affecting lung cancer development in IPF patients.
|
aHR |
Lower .95 |
Upper .95 |
p-value |
Statin compliance |
0.6561 |
0.4807 |
0.8954 |
< 0.001 |
Statin use |
0.6329 |
0.5260 |
0.7614 |
< 0.001 |
Sex – female |
0.4311 |
0.3332 |
0.5576 |
< 0.001 |
Age at first diagnosis of IPF |
1.0455 |
1.0357 |
1.0554 |
< 0.001 |
BMI |
1.0057 |
0.9762 |
1.0362 |
0.707 |
Blood pressure |
|
|
|
|
Systolic |
0.9995 |
0.9922 |
1.0069 |
0.366 |
Diastolic |
0.9995 |
0.9880 |
1.0111 |
0.934 |
Smoking history (ex + current) |
1.5460 |
1.3911 |
1.7183 |
< 0.001 |
Alcohol frequency |
0.9982 |
0.9315 |
1.0696 |
0.959 |
Exercise frequency |
0.9537 |
0.8886 |
1.0235 |
0.188 |
Comorbidities |
|
|
|
|
Liver diseases |
1.2332 |
0.6567 |
2.3158 |
0.514 |
Hypertension |
1.0478 |
0.8229 |
1.3342 |
0.705 |
Stroke |
1.7280 |
0.7670 |
3.8930 |
0.187 |
Heart diseases |
1.0514 |
0.6454 |
1.7129 |
0.84 |
Diabetes |
1.0218 |
0.7330 |
1.4246 |
0.899 |
Cancers |
0.7224 |
0.3960 |
1.3180 |
0.289 |
We also analyzed the risk factors for mortality in IPF patients after adjusting for demographic variables using multivariate Cox regression (
Table 4). Statin use (aHR 0.43, 95% CI 0.39–0.46,
p < 0.001), female sex (aHR 0.67, 95% CI 0.61–0.73,
p < 0.001), higher exercise frequency (aHR 0.93, 95% CI 0.90–0.96,
p < 0.001), and diabetes (aHR 0.78, 95% CI 0.69–0.88,
p < 0.001) were associated with reduced risk of mortality in IPF patients. In contrast, older age at IPF diagnosis (aHR 1.07, 95% CI 1.07–1.08,
p < 0.001) and smoking history (aHR 1.06, 95% CI 1.01–1.11,
p = 0.0182) were associated significantly with shorter OS in IPF patients.
4. Discussion
We identified clinical impacts of regular consecutive statin use in IPF patients who had both delayed lung cancer and prolonged OS. In Cox proportional hazard regression models, higher statin compliance, statin use, and female sex were independently associated with reduced risk of lung cancer, and older age at diagnosis of IPF and smoking history were associated with higher risk of lung cancer in IPF patients. For OS, statin use, female sex, higher exercise frequency, and diabetes were associated with longer survival. In contrast, older age at diagnosis of IPF and smoking history were associated with shorter OS in IPF patients.
Aside from the well-known lipid-lowering effect, statins were reported to have anti-cancer effects through various pathways including inhibition of inflammation, immunomodulation, and angiogenesis [
7]. Recently, the long-term use of statins was reported to reduce the risk of mortality in patients with lung cancer [
30]. In a meta-analysis, statin use after diagnosis of lung cancer had a survival benefit for OS (HR 0.68, 95% CI 0.51–0.92) compared to those using statins before diagnosis.[
31] Statins were also associated with prolonged survival in non-small cell lung cancer (NSCLC) patients treated with epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI)s.[
32] Furthermore, statins can overcome EGFR-TKI resistance in patients with lung cancer harboring KRAS mutation, and they provided an increased response rate in lung cancer patients previously treated with nivolumab [
33,
34]. In contrast, there was no significant difference in efficacy between a group with addition of simvastatin to afatinib and a group with afatinib alone in patients with non-adenocarcinomatous NSCLC.[
35]
IPF has a progressive clinical course including a decline in pulmonary function, decrease in vital capacity, and diffusing capacity for carbon monoxide (DLCO).[
36] Further, lung cancer is a common morbidity of IPF with a prevalence of 4.4% to 13%.[
37] If lung cancer develops in IPF patients, treatment modalities are limited regardless of lung cancer stage. The treatment goal for early-stage resectable lung cancer is complete remission. Standard curative treatment for patients with NSCLC is lobectomy.[
38] Lung resection including lobectomy can cause a reduction in lung function, acute exacerbation (AE) of IPF, and acute respiratory distress syndrome (ARDS).[
39] For patients who are not surgical candidates due to medical reasons (e.g., cardiac or pulmonary failure), stereotactic ablative radiotherapy is a potential treatment option with comparable efficacy to surgery.[
40] However, severe pulmonary toxicity such as radiation pneumonitis or ARDS was reported in 1.5–20% of patients who received stereotactic ablative radiotherapy in lung cancer patients with IPF.[
41] Drug pneumonitis and IPF AE often recur in the advanced stages of lung cancer in IPF patients.[
42,
43] In a retrospective study, the incidence of lung cancer was reduced in IPF patients treated with pirfenidone.[
44] However, no definite conclusion can be drawn from that retrospective study. For these reasons, strategies for early diagnosis and prevention of lung cancer are needed in IPF patients.
In our study, stain use was associated with delayed time from IPF diagnosis to lung cancer development. In a randomized controlled trial, there was a lower forced vital capacity (FVC) decline in IPF patients who received statins at baseline versus those who did not.[
45] Also, statin use attenuated the decline in lung function in the elderly, and the effect of statins was estimated to be beneficial regardless of smoking status even though the size of the improvement varied among smoking groups.[
19] In IPF patients, risk factors for lung cancer included being male, current smoking at IPF diagnosis, and rapid annual decline of 10% or more in FVC.[
36] Decreased lung function is linked to increased inflammation and oxidative stress, and anti-inflammatory properties of statins were investigated in respiratory disease. In an animal study, statins reduced neutrophil levels in lung tissue damaged by lipopolysaccharides.[
46] Also, statins protected against smoking-induced lung damage and showed anti-inflammatory effects on the lung.[
47] In lung transplant recipients, the levels of neutrophils and lymphocytes in the bronchoalveolar lavage of statin users were reduced compared with nonusers.[
48] The inhibitory effect of statin on Ras farnesylation was well investigated. Kras alleles are activated in human lung adenocarcinomas, and inhibition of this is important in lung cancer prevention.[
49] Also, lovastatin inhibits cell proliferation, cell cycle progression, and apoptosis in NSCLC cells through minichromosome maintenance (MCM) 2, involved in G1/S cell cycle inhibition.[
50] Inflammation affects many aspects of malignancy including the proliferation and survival of cancer cells, angiogenesis, tumor metastasis, and tumor response to chemotherapeutic drugs.[
51] The exact mechanism of the preventive effect of statin on lung cancer development in IPF patients is not fully understood, but it is believed that anti-inflammation actions on fibrotic lungs and the resulting lower decline in lung function may delay the occurrence of lung cancer. However, in meta-analysis, non-significant decrease of total lung cancer risk was observed among all statin users (RR = 0.89, 95% CI 0.78–1.02).[
52] Further randomized controlled trials and high quality cohort studies are needed to confirm this association.
In our study, statin users had lower risk of death among IPF patients. This finding is consistent with a previous study. Kreuter et al. reported that statins might have a beneficial effect on the clinical outcomes of IPF patients including lower risks of death, six-minute walk distance decline, all-cause hospitalization, and IPF-related mortality.[
18] Repetitive alveolar epithelial injury triggered the early development of IPF. The exact etiology of IPF is unknown, and all stages of fibrosis are accompanied by innate and adaptive immune responses.[
53] Modulatory effects of statins on pathways of fibrosis were investigated by in vitro studies. Exposure to statins resulted in a reversible and time-dependent change in cell morphology in human renal fibroblasts.[
54] Fluvastatin inhibits TGF-ß1-induced thrombospondin-1 expression in coronary artery smooth muscle cells.[
55] However, statin use and all-cause mortality in IPF patients showed controversial results based on a statistical analysis.[
56] A prospective cohort study with dosage of statin, statin adherence, and use of concurrent antifibrotics is needed to confirm beneficial effects of statin therapy in IPF patients.
In our study, higher exercise frequency decreased all-cause mortality by 8% in IPF patients. It is well known that cardiopulmonary exercise tests and six-min walk tests provide prognostic value of mortality in patients with IPF. [
57] Decreased physical activity was associated with lower progression-free survival (HR 12.1, 95% CI, 1.9–78.8, P = 0.009) in IPF patients. Lower quadriceps strength and higher depression scores contribute to lower physical activity. [
58] Pulmonary rehabilitation using exercise training is effective for improving exercise capacity, dyspnea, and quality of life in IPF patients. [
59] Also, pulmonary rehabilitation noncompletion and nonresponse were associated independently with increased one-year all-cause mortality in IPF patients. [
60] Even without active intervention such as respiratory rehabilitation, life style behaviors such as shorter daily sitting and longer weekly walking were associated with reduced hospitalization and mortality risks in patients with IPF. [
61] Although the exercise frequency of our study was collected using a subjective self-report, it supports the previous study findings that exercise can lower the mortality of IPF patients based on large-scale cohort data.
Interestingly, not only did the exercise frequency reduce all-cause mortality, but comorbid diabetes showed a 22% risk reduction of death in IPF patients. The biology of aging may influence the susceptibility to lung fibrosis in the elderly, increasing the incidence of IPF in patients over 60 years of age [
62]. Relatively older populations with IPF have variable comorbidities such as hypertension, cardiovascular diseases, and diabetes. Type 2 diabetes mellitus (DM) is a common underlying disease in many IPF patients [
63]. DM is a systemic metabolic disease characterized by persistent hyperglycemia, and the lungs are targeted by diabetic micro-vascular damage [
64]. Epidemiological research reported that diabetes is a risk factor for IPF, with the prevalence of IPF accompanied by DM estimated to be 10–42% even when excluding cases treated with glucocorticoids [
65,
66]. Further, DM was reported to be a risk factor with higher mortality in an IPF population (HR 2.5, 95% CI 1.04–5.9) [
67]. Contrary to the prior study, our study suggested that DM was associated with reduced risk of mortality in IPF patients. This may be partly due to diabetic medications. Metformin is the first-choice of treatment for glycemic control [
68]. Aside from the glucose lowering effect, metformin was involved in anti-fibrotic physiology associated with AMPK activation and showed an inhibitory effect in myofibroblasts differentiation [
69]. Also, GLP-1 receptor agonists were found to have anti-pulmonary fibrotic effects and alleviated bleomycin-induced lung damage and fibrosis through inactivation of nuclear factor kappa-B in animal studies. [
70] In our study, we did not conduct an investigation of diabetic drugs, so it was not possible to confirm whether mortality was reduced by DM or diabetic drugs. Further investigations through a survey on individualized diabetic medication intake are necessary to determine the effect of DM on mortality in IPF patients.
The limitations of our study should be recognized. First, as the study design was retrospective and based on a large population-based cohort, there is the possibility of selection bias of confounding factors that might have influenced the study results. Second, we tried to include drug compliance, but the true medication adherence could not be estimated. Instead, we performed a mathematical assessment of drug compliance based on the total days of statin prescribed divided by the study period. Third, the dose and the different potency of statin were not included as confounding factors. Also, we did not consider antifibrotics (including pirfenidone and nintedanib) as confounding factors. Lastly, we did not include the severity and status of IPF based on pulmonary function (e.g., FVC, DLCO). To identify further effects of statin use on lung cancer development and mortality in IPF patients, a well-designed large scale prospective study is necessary.
Author Contributions
Conceptualization, H.S.K. and Y.J.L.; Data curation, H.S.K., N.Y.K., J.W.R., and Y.J.L.; Formal analysis, H.S.K. and N.Y.K.; Funding acquisition, H.S.K.; Investigation, H.S.K., N.Y.K., Y.H.K., and Y.J.L.; Methodology, H.S.K. and N.Y.K.; Project administration, H.S.K., Y.H.K., and Y.J.L.; Resources, H.S.K. and N.Y.K.; Software, N.Y.K.; Supervision, H.S.K., S.S.K., and Y.H.K.; Validation, H.S.K., N.Y.K., J.H.N., and Y.H.K.; Visualization, N.Y.K..; Writing—original draft, H.S.K., E.G.L., Y.J.L., J.W.R., and Y.H.K.; Writing—review and editing, H.S.K., Y.J.L, S.S.K., and Y.H.K. All authors have read and agreed to the published version of the manuscript.