Statins Are Associated With a Reduced Risk of Hepatocellular Carcinoma in a Large Cohort of Patients With Diabetes

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1 GASTROENTEROLOGY 2009;136: Statins Are Associated With a Reduced Risk of Hepatocellular Carcinoma in a Large Cohort of Patients With Diabetes HASHEM B. EL SERAG,* MICHAEL L. JOHNSON, CHRISTINE HACHEM,* and ROBERT O. MORGANA* *Sections of Gastroenterology and Health Services Research at the Michael E. DeBakey Veterans Affairs Medical Center and Baylor College of Medicine, Houston, Texas; and Department of Clinical Sciences and Administration, University of Houston, College of Pharmacy, Houston, Texas Background & Aims: Experimental studies indicate a potential cancer prevention effect for statins. Given the increasing prevalence of statin use, and the increasing incidence of hepatocellular carcinoma (HCC), the potential association between statins and HCC is an important issue to examine. Methods: We conducted a matched case-control study nested within a cohort of patients with diabetes. Cases comprised incident HCC at least 6 months after entry in the cohort. Controls were identified by incidence density sampling from patients who remained at risk at the date of the HCC diagnosis matched by age and sex. We identified filled statin prescriptions as well as several potential confounding conditions, medications, as well as propensity score to use statins. Odds ratios (ORs) as estimates of the relative risk for HCC associated with statin use and 95% confidence intervals were obtained using conditional logistic regression. Results: We examined 1303 cases and 5212 controls. The mean age was 72 years and 99% were men. A significantly smaller proportion of cases (34.3%) had at least one filled prescription for statins than controls (53.1%). There were no significant associations between HCC and nonstatin cholesterol- or triglyceride-lowering medications. The OR for any statin prescription was 0.46 (95% confidence interval, ) and the adjusted OR was 0.74 (95% confidence interval, ). To reduce the potential confounding effect of existing liver disease, we ran the analyses in a subgroup of patients without recorded liver disease; the ORs were slightly attenuated but remained highly significant for any statin prescription (0.63; 95% confidence interval, ). Conclusions: Statin use is associated with a significant reduction in the risk of HCC among patients with diabetes. Interest has increased in the potential cancer-preventive effect of cholesterol-lowering 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, commonly known as statins. Some but not all epidemiologic studies have reported a modest statin-related reduction in the risk of several malignancies, including colon, breast, pancreas, and prostate cancer. 1 4 Several general mechanisms have been proposed for this possible effect, including the disruption of malignant cell growth by inhibition of downstream products of the mevalonate pathway, an important activator of a number of cellular proteins, including K-ras. 4 Statins also inhibit the activation of the proteosome pathway, limiting the breakdown of both p21 and p27, thus allowing these molecules to exert their growthinhibitory effects. 3,5 The association between statin use and the risk of hepatocellular carcinoma (HCC) is unclear. HCC is a highly fatal malignancy that has been increasing in several regions of the world, including the United States. 6 Experimental as well as indirect human data suggest that statins exert a beneficial action, reducing the progression of HCC. 6,7 One study reported that statins inhibit the proliferation of HCC by inducing apoptosis and G 1 /S cell-cycle arrest. 8 Pravastatin has been shown to reduce progression and metastatic diffusion of established HCC in a rat model, an action that could be linked to the decreased matrix metalloproteinase activity. 9 Similar findings have been suggested in a clinical trial of 91 patients with advanced HCC in which the median survival of 18 months of those on pravastatin was twice that of controls (P.006). 10 Lastly, there is also a suggestion that hepatitis C virus (HCV)-RNA replication is disrupted in vitro as well as in vivo studies by high concentrations of statins On the other hand, statins have been linked in rodent studies to hepatic adenomas and carcinomas. 14,15 The association between statins and cancer, including HCC, were examined in clinical trials of statins in which association with cancer was a secondary end point. In at least 2 trials, investigators found a statistically nonsignificant inverse association between statin use and total cancer incidence. 16,17 However, a meta-analysis 18 of 5 trials of statins and cardiovascular disease reported no association between statin use and risk of incident cancers. The number of HCC cases in these trials was not specifically mentioned, and it was likely very small (if existent). Clearly, there is not enough evidence to support Abbreviations used in this paper: OR, odds ratio; VA, Veterans Affairs by the AGA Institute /09/$36.00 doi: /j.gastro

2 1602 EL SERAG ET AL GASTROENTEROLOGY Vol. 136, No. 5 a clinical trial in patients at this time, especially because statins can be hepatotoxic 19 ; therefore, epidemiologic evidence for a cancer-protective effect is required. To meet that need, we undertook an epidemiologic study in a large cohort of diabetics, whose risk of HCC is higher than average, to characterize the relationship between statin use and HCC and other liver disease. Methods We conducted a nested case-control study within a large cohort of patients with diabetes mellitus identified during the calendar years , in the Department of Veterans Affairs (VA) national databases, including the Patient Treatment files, Outpatient Clinic files, Pharmacy Benefits Management files, and Beneficiary Identification Records Locator System death files. The institutional review boards of Baylor College of Medicine and the Michael E. DeBakey VA Medical Center in Houston, TX, approved this study. The Patient Treatment Files contain inpatient records, including date of admission and discharge, and up to 10 discharge diagnoses (by International Classification of Diseases 9th revision clinical modification codes) for all hospitalizations at any of the more than 150 VA hospitals in the United States. The Outpatient Clinic files contain similar data for all outpatient encounters at any VA facility. We identified patients in Outpatient Clinic files and Patient Treatment Files with International Classification of Diseases 9th revision codes , 357.2, 362.0, and as having diabetes. We used an additional measure to confirm the diabetes classification by searching national VA Pharmacy Benefits Management files for the calendar years for oral diabetes medications (HS502), insulin (HS501), or blood glucose monitoring supplies (in drug class DX900). Each cohort member s entry date was the earliest qualifying inpatient or outpatient event associated with diabetes. The VA diabetes cohort was linked with Medicare files (calendar years ) to maximize the probability of capturing health care encounters among patients who were treated by both the VA and Medicare. Finally, we used the date of death recorded in the VA Beneficiary Identification Records Locator System death file. The Patient Treatment Files and Beneficiary Identification Records Locator System death files together reportedly capture 90% 95% of deaths in VA users. 17,18 Cases were defined as patients with incident HCC identified by International Classification of Diseases 9th revision code recorded in VA or Medicare files at least 6 months after the entry date into the diabetes cohort. We limited eligible cases to those diagnosed between January 1, 2001, and December 30, 2002, to allow having 2 4 years of prior exposure with complete Pharmacy Benefits Management and Medicare data. Controls were identified by incidence density sampling from subjects who remained at risk of HCC at the date of the HCC diagnosis for the case (index date). 20 This entailed matching on age ( 1 year), sex, and the date of entry into the diabetes cohort ( 30 days). Controls could not have a diagnosis of HCC within 6 months of the matched case s HCC index date. Controls were selected randomly with potential for replacement. That is, one subject could be a control for more than one case, and any one control could later ( 6 mo) become a case if diagnosed with HCC. We excluded patients without any VA pharmacy use. For cases and controls with dual VA and Medicare enrollment, we included only patients with continuous enrollment in non HMO Medicare (defined as 75% of the duration between diabetes cohort entry and HCC index dates). These patients are likely to have complete VA prescription information (which is the most likely source of prescription drugs, even in dual VA Medicare users 21 and should have virtually all of their health care activities captured either in VA or in Medicare records). Exposure to Statins We identified patients who filled outpatient prescriptions for statins in any VA pharmacy between January 1, 1999, and the index date for cases and controls. Statin prescriptions were limited to those available in the VA, by formulary or nonformulary request, including simvastatin, lovastatin, atorvastatin, fluvastatin, pravastatin, and cerivastatin. We collected the dates of filled prescriptions, the daily dose, the number of days supplied, and the number of pills per prescription. We collected similar information on nonstatin lipid-lowering medications (cholestyramine, colesevelam, colestipol, ezetimibe, niacin), triglyceride-lowering medications (clofibrate, fenofibrate, gemfibrozil), and diabetes medications (insulin, sulfonylureas, thiazolidinedione). Potential Confounders We identified any liver disease defined by the following diagnoses recorded between January 1, 1997, and the HCC index date: alcoholism (291.xx, 303.0x, 303.9x, 305.0x), cirrhosis (571.2, 571.5, 571.6), hepatitis C infection (070.41, , , , V02.62), hepatitis B infection (070.22, , , , V02.61), obesity (278), and alcoholic liver disease (571.0, 571.1, 571.2, 571.3). We also identified filled prescriptions for HCV treatment, hepatitis B virus (HBV) treatment, aspirin, nonsteroidal anti-inflammatory drugs, and angiotensinconverting enzyme inhibitors. A subset with severe liver disease was identified with cirrhosis codes (571.2, 571.5, 571.6, 572.3). We also adjusted for filled diabetes medications. Given the observational nature of the study, confounding by indication is a major concern and therefore we attempted to adjust for the propensity to give statins. We constructed a logistic regression model to generate a propensity score that expresses the likelihood of receiving a statin among members of the diabetes cohort. The outcome variable in the propensity model is any filled

3 May 2009 STATINS AND REDUCED RISK OF HCC 1603 statin prescriptions, and the covariates were chosen, based on their biological plausibility and their significance in analyses (P.1), and entered in a stepwise logistic regression model. The covariates that constituted the final model were coronary artery disease, myocardial ischemia, liver disease, obesity, and diabetic nephropathy (data not shown). We subsequently adjusted for the propensity score in the conditional logistic regression models examining filled statin prescriptions with the risk of HCC (see later). 22 Statistical Analyses Differences in covariate distribution between cases and controls were determined using chi-squared tests for categoric variables and t tests for continuous variables. We estimated odds ratios (ORs) as estimates of the relative risk for HCC associated with statin use and their accompanying 95% confidence intervals using conditional logistic regression. In addition to matching variables (age, sex, date of entry in the diabetes cohort), adjustment was performed for possible confounders including race, HCV infection, alcoholic liver disease, cirrhosis, alcoholism, as well as a combination of factors such as HCV plus alcoholic liver disease. We adjusted for the propensity score by adding the propensity score as a covariate in the final model examining the association between statins and HCC, and by conducting a stratified analysis in which the association between statins and HCC was examined separately in 2 groups of patients with a high and low propensity to receive statin. To examine potential effect modifiers, we conducted analyses stratified by groups with and without any liver disease, and by groups with and without cirrhosis. The primary exposure was a filled prescription for any statin before the index HCC date. To reduce the possibility of confounding by indication, we also assessed any statin prescription, excluding those given in the 1 year directly preceding the index HCC date. To examine the duration-effect relationship, we evaluated the effect of the number of prescriptions fills/refills (0, 1 3, 3) and the cumulative duration of any statin prescriptions examined in the following categories: 0 180, , , , and more than 720 days compared with the reference group (no statin prescription). We also examined these duration categories, excluding the 1 year preceding the index HCC date in each case. We evaluated the OR by the dose-duration and the total number of prescriptions of simvastatin, which was the most commonly used statin in the study population. We computed the average daily dose of each filled simvastatin prescription (strength multiplied by the average daily quantity), the dose duration for the prescription (average daily dose multiplied by days of use before HCC index date), and subsequently the cumulative dose duration before the HCC index date (sum of dose durations over all simvastatin fills). For any 2 overlapping prescriptions, we added the dose duration of the first prescription to that of the second prescription if the overlap period was less than 30 days, assuming that patients may have used these prescriptions sequentially. For an overlap of greater than 30 days, we deducted the dose duration of the first prescription for the period after the start of the second prescription, assuming that the second prescription replaced the first one. We compared the distribution of dose duration for simvastatin measured as quartiles between cases and controls. Chart Validation We conducted a nested chart validation of the cases or control status as well as statin exposure at the Michael E. DeBakey Veterans Affairs Medical Center in Houston, TX, and the St. Louis VA in St. Louis, MO. We identified 129 patients (34 cases, 95 controls) who had at least one health care encounter at either VA between 1999 and A trained clinician blinded to the case/ control and statin exposure status reviewed the electronic medical records. HCC diagnosis was identified from progress notes, radiology, laboratory, or pathology reports. Statin use was defined as filled prescriptions within the study period. Underlying etiology (HCV, HBV, alcoholic liver disease, fatty liver) for HCC cases also was identified. Results The study population consisted of 1303 cases with HCC diagnosed between January 1, 2001, and December 31, 2002, and 5212 controls without HCC matched on age, sex, and incidence density (ratio, 1:4). Mean age was 72 years. Most subjects (99%) were men, and 13% were African Americans. As expected from incidence density sampling and matching, cases and controls had no significant differences in age and duration between entry and index dates (Table 1). The case group had significantly higher proportions of liver disease, HCV treatment, and HBV treatment; however, both were quite low. The case group had a slightly lower proportion of patients with filled prescriptions for aspirin and angiotensin-converting enzyme inhibitors. During a mean exposure period of 2.4 years that preceded index dates for cases and controls, approximately 49% had a recorded filled statin prescription, 4% had nonstatin cholesterol-lowering drugs, and 9% had triglyceride-lowering drugs. In cases and controls, 41.6% of whom had had a prescription filled for at least 6 months, 32.3% had it filled for at least 12 months, and 22.7% had it filled for at least 18 months. The mean overall duration of any given statin prescription was days (SD, days). Liver disease recorded as early as January 1, 1997, or within 4 6 years before the index date, was recorded in a larger population of cases (67.4%) than controls (8.7%). The propensity score (to use statins) was generated from the model that contained coronary artery disease,

4 1604 EL SERAG ET AL GASTROENTEROLOGY Vol. 136, No. 5 Table 1. Demographic Factors and Filled Prescription Data in Cases With HCC and HCC-Free Matched Controls Cases (n 1303) Controls (n 5212) Variable N % N % P value Mean age, y Men Race African American White Mean duration between entry and index date, y Drugs Any statin filled prescriptions filled prescriptions Simvastatin Nonstatin cholesterol-lowering drug(s) Triglyceride-lowering drug(s) Aspirin Aspirin or NSAIDs HCV treatment HBV treatment ACE inhibitors Liver disease HCV HBV Alcoholic liver disease Cirrhosis Any liver disease NOTE. Cases and controls were matched on age, sex, and incidence density. ACE, angiotensin-converting enzyme; NSAID, nonsteroidal anti-inflammatory drug. myocardial ischemia, liver disease, obesity, and diabetic nephropathy as covariates, and was categorized into 3 equal tertiles: low propensity (found in 12.6% of the study population), medium propensity (in 39.1%), and high propensity (in 48.3%). A propensity score categoric variable (high propensity vs other) was used as a covariate in all the final models examining the statin-hcc associations. Further, the statin-hcc models were conducted as a sensitivity analysis in a group limited to patients with high propensity score. We found high accuracy for our definitions of casecontrol as well as statin prescriptions. After reviewing a sample of medical records at the Michael E. DeBakey Veterans Affairs Medical Center, we found all 95 controls were classified correctly as not having HCC. All 57 patients who had filled prescription statins recorded in administrative records were identified correctly, and 65 patients classified as having had no statin prescriptions during the calendar years in administrative data also were identified correctly (100% positive predictive value and 100% negative predictive value for administrative data). Of cases identified as HCC in the VA Medicare dataset, 89% were identified correctly as HCC by chart reviews. The underlying etiology in HCC cases was HCV (23%), alcoholic liver disease only (23%), and fatty liver disease (38%), but there was no mention of risk factors or cirrhosis in 15%. The proportion of patients with filled statin (or simvastatin) prescriptions was significantly lower among cases than controls (Table 1). The difference was mainly in the proportion of patients receiving more than 3 fills/refills, which was significantly lower in cases than in controls (18.2% vs 43.5%). Among those with at least one statin prescription, controls had an average of 9.9 (SD, 7.1) fills/refills as compared with 9.4 (SD, 6.9) in cases. On the other hand, there were no significant differences between cases and controls in the proportion of patients with filled prescriptions for triglyceride-lowering and nonstatin cholesterol-reducing medications. Having filled prescriptions for any statin was associated with a reduced risk of HCC in the primary analyses as well as in analyses stratified by the presence of known liver disease of any kind before HCC (Table 2). These significant associations were observed in conditional logistic regression models and also were present but attenuated in the models adjusted for HCV, alcoholic liver disease, cirrhosis, alcoholism, race, HCV treatment, aspirin/nonsteroidal anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, and propensity score. The relative odds of HCC were reduced in all groups (range, ). The lowest relative risk for all patients (adjusted and ) as well as for patients without liver disease () occurred when the duration of filled prescriptions was at least 18 months. When the

5 May 2009 STATINS AND REDUCED RISK OF HCC 1605 Table 2. Relative Risk for HCC Associated With Use of Any Statin in Cases With HCC and Controls Without HCC: Results of Conditional Logistic Regression Models OR (95% confidence interval) Duration of statin prescription filling All patients, All patients, adjusted a Patients with liver disease, (879 cases, 455 controls) Patients without liver disease, (424 cases, 4757 controls) Any duration 0.46 ( ) 0.74 ( ) 0.52 ( ) 0.63 ( ) Excluding 1 year before 0.48 ( ) 0.79 ( ) 0.48 ( ) 0.68 ( ) index date 1 3 prescriptions 0.52 ( ) 0.73 ( ) 0.62 ( ) 0.68 ( ) More than 3 prescriptions 0.44 ( ) 0.75 ( ) 0.49 ( ) 0.62 ( ) a Adjusted for alcoholism, alcoholic liver disease, cirrhosis, HCV infection, HBV infection, race, HCV treatment, propensity to use statins, asprin/nonsteroidal anti-inflammatory drugs, and angiotensin-converting enzyme inhibitors. analysis excluded statin prescriptions recorded within the 1 year preceding HCC diagnosis, the associations between statins and HCC were less strong. Running the same analysis using simvastatin alone produced similar reductions in relative risk of HCC (relative risk values varied between 0.45 and 0.72) (Table 3). As with the analyses that used any statin, the reduced relative risk values in the adjusted population were less than those in the population. In both analyses (Tables 2 and 3) but especially those for simvastatin, there was a trend toward lower ORs (ie, more risk reduction) with having more than 3 filled prescriptions than with 1 3 prescriptions as compared with no statins. In an analysis restricted to patients with cirrhosis (data not shown), risk estimates for statins were of similar magnitude to those observed in the primary analysis. However, because of the small number of subjects (367 cases and only 86 controls), there was no statistical significance. In another analysis restricted to patients in the highest tertile for propensity score to use statins, risk estimates for statins also persisted in direction and significance; for example, the OR associated with having 1 3 filled statin prescriptions was 0.63 (95% confidence interval, ) and that of using more than 3 filled statin prescriptions was 0.67 (95% confidence interval, ). When the duration of prescription filling was divided into mutually exclusive periods, the reduced relative risk values for any statin or for simvastatin persisted (Table 4). There was a weak trend toward duration response relationship between statin and HCC risk. For any statin or for simvastatin alone, the association between the statin and HCC was weakest with the shortest duration of filled prescriptions. For example, for any statin the 0.59 relative risk at less than 6 months was the highest value of the periods measured; however, there was no significant or consistent trend of reduction with longer duration (0.40, 0.57, 0.42, and 0.39) for 6 12, 12 18, 18 24, or more than 24 months, respectively. When exposure to simvastatin was measured in quartiles of dose duration, the lowest dose duration produced weaker associations with HCC than higher dose duration. Some of the associations with the lowest dose duration were not significant in the analyses stratified by liver disease status. Likewise, the magnitude of inverse association with HCC was least for the quartile with the lowest dose and duration (OR, 0.52; confidence interval, ) than the higher quartiles; however, there was no discernible trend in the OR values of the second, third, and fourth quartiles that followed (0.49, 0.41, and 0.44, respectively). Finally, we determined if the observed associations were unique to statins as compared with other lipidlowering medications. In the analyses shown in Table 5, there were no significant associations between HCC and either triglyceride- or nonstatin cholesterol-lowering drugs. Table 3. Relative Risk for HCC Associated With Having Filled Prescriptions of Simvastatin in Cases With HCC and Controls Without HCC OR (95% confidence interval) Duration of simvastatin prescription filling All patients, All patients, adjusted a Patients with liver disease, (879 cases, 455 controls) Patients without liver disease, (424 cases, 4757 controls) Any duration 0.47 ( ) 0.64 ( ) 0.51 ( ) 0.60 ( ) Excluding 1 year before index 0.48 ( ) 0.65 ( ) 0.46 ( ) 0.71 ( ) date 1 3 prescriptions 0.59 ( ) 0.72 ( ) 0.63 ( ) 0.72 ( ) 3 prescriptions 0.48 ( ) 0.61 ( ) 0.45 ( ) 0.63 ( ) a Adjusted for alcoholism, alcoholic liver disease, cirrhosis, HCV infection, HBV infection, race, HCV treatment, propensity to use statins, asprin/nonsteroidal anti-inflammatory drugs, and angiotensin-converting enzyme inhibitors.

6 1606 EL SERAG ET AL GASTROENTEROLOGY Vol. 136, No. 5 Table 4. Relative Risk for HCC Associated With the Effect of Cumulative Duration and Dose Duration of any Filled Statin Prescription Examined in Mutually Exclusive Periods OR (95% confidence interval) All patients, All patients, adjusted a Patients with liver disease, (879 cases, 455 controls) Patients without liver disease, (424 cases, 4757 controls) Any statin duration, mo ( ) 0.88 ( ) 0.77 ( ) 0.79 ( ) (83 cases/394 controls) (83 cases/394 controls) (52 cases/32 controls) (31 cases/362 controls) ( ) 0.56 ( ) 0.40 ( ) 0.50 ( ) (69 cases/494 controls) (69 cases/494 controls) (44 cases/34 controls) (25 cases/460 controls) ( ) 0.88 ( ) 0.43 ( ) 0.78 ( ) (85 cases/427 controls) (85 cases/427 controls) (53 cases/39 controls) (32 cases/388 controls) ( ) 0.71 ( ) 0.43 ( ) 0.52 ( ) (74 cases/491 controls) (74 cases/491 controls) (44 cases/37 controls) (30 cases/454 controls) ( ) 0.75 ( ) 0.51 ( ) 0.63 ( ) (136 cases/960 controls) (136 cases/960 controls) (72 cases/65 controls) (64 cases/895 controls) Simvastatin duration, mo ( ) 0.80 ( ) 0.80 ( ) 0.80 ( ) (72 cases/329 controls) (72 cases/329 controls) (46 cases/29 controls) (26 cases/300 controls) ( ) 0.51 ( ) 0.40 ( ) 0.45 ( ) (59 cases/405 controls) (59 cases/405 controls) (40 cases/28 controls) (19 cases/377 controls) ( ) 0.73 ( ) 0.40 ( ) 0.78 ( ) (64 cases/333 controls) (64 cases/333 controls) (41 cases/32 controls) (23 cases/301 controls) ( ) 0.58 ( ) 0.45 ( ) 0.51 ( ) (52 cases/359 controls) (52 cases/359 controls) (31 cases/27 controls) (21 cases/332 controls) ( ) 0.61 ( ) 0.41 ( ) 0.72 ( ) (95 cases/640 controls) (95 cases/640 controls) (45 cases/43 controls) (50 cases/597 controls) Simvastatin dose duration 1st quartile lowest dose-duration 0.52 ( ) 0.67 ( ) 0.75 ( ) 0.74 ( ) (92 cases/502 controls) (92 cases/502 controls) (56 cases/37 controls) (36 cases/465 controls) 2nd quartile 0.49 ( ) 0.67 ( ) 0.55 ( ) 0.60 ( ) (89 cases/517 controls) (89 cases/517 controls) (58 cases/38 controls) (31 cases/479 controls) 3rd quartile 0.41 ( ) 0.56 ( ) 0.24 ( ) 0.59 ( ) (78 cases/528 controls) (78 cases/528 controls) (47 cases/45 controls) (31 cases/483 controls) 4th quartile highest dose-duration 0.44 ( ) 0.68 ( ) 0.40 ( ) 0.67 ( ) (83 cases/519 controls) (83 cases/519 controls) (42 cases/39 controls) (41 cases/480 controls) a Adjusted stepwise. Discussion In this nested case-control study of patients with diabetes, we found a significant inverse association between having statin prescriptions filled and the risk of developing HCC. There was a trend toward stronger risk reduction with longer and more frequent statin prescriptions. Reduced HCC risk was similar, whether the prescriptions were for simvastatin or any other statin dispensed. The risk reduction observed with statin ranged between 25% and 40%. These findings largely persisted in analyses that adjusted for propensity to use statins, excluded use within 1 year before HCC diagnosis, and analyses in patients with as well as without known liver disease or cirrhosis. There were no significant associations between HCC risk and filling prescriptions for nonstatin cholesterol-reducing or triglyceride-lowering medications. A number of potential mechanisms responsible for the effect of statins in reducing risk of HCC have been investigated, including inhibiting downstream products of the mevalonate pathway, primarily geranylgeranyl pyrophosphate and farnesylpyrophosphate. Derivatives of the mevalonate pathway geranylgeranyl pyrophosphate and farnesylpyrophosphate are important in the activa- Table 5. Relative Risk for HCC Associated With Having Filled Prescriptions of Nonstatin Cholesterol Lowering Medications in Cases With HCC and Controls Without HCC OR (95% confidence interval) Type of prescription filled All patients, All patients, adjusted a Patients with liver disease, (879 cases, 455 controls) Patients without liver disease, (424 cases, 4757 controls) Nonstatin cholesterol-lowering drug(s) Any () 1.04 ( ) 0.92 ( ) 1.20 ( ) 0.60 ( ) Excluding 1 year before index date 0.90 ( ) 0.78 ( ) 1.25 ( ) 0.67 ( ) Triglyceride-lowering drug(s) Any () 0.81 ( ) 1.10 ( ) 0.68 ( ) 0.82 ( ) Excluding 1 year before index date 0.83 ( ) 1.13 ( ) 0.76 ( ) 0.86 ( ) a Adjusted for alcoholism, alcoholic liver disease, cirrhosis, HCV infection, HBV infection.

7 May 2009 STATINS AND REDUCED RISK OF HCC 1607 tion of a number of cellular proteins, including small guanosine-5=-triphosphate binding proteins, such as K- ras, and the Rho family. 1,23,24 Statins interfere with the production of geranylgeranyl pyrophosphate and farnesylpyrophosphate and disrupt the growth of malignant cells, eventually leading to apoptosis. 4 It also is believed that p21 and p27 are cyclin-dependent kinase inhibitors that inhibit the growth of cancerous cells. Statins also are thought to inhibit the activation of the proteosome pathway, limiting the breakdown of both p21 and p27, allowing these molecules to exert their growth-inhibitory effects and in turn retard cancer cell mitosis. 3,5 Statins also have been shown to inhibit proliferation of stellate cells and their production of collagens in a dosedependent manner. 25,26 Finally, statins may have an effect specific to HCV. Recently, it has been shown that HCV replication depends in part on geranylgeranylation of a host protein but high concentrations of statins can disrupt HCV-RNA replication. The effect presumably was owing to severe depletion of mevalonic acid, which in turn led to low cellular levels of geranylgeranyl pyrophosphate, the substrate for the geranylgeranyl-transferase. 13 If physicians are less likely to prescribe statins because of their hepatotoxicity, patients with liver disease, especially those with severe liver disease, are less likely to be prescribed statins, which in a study such as ours could lead to a spurious inverse association between statin use and HCC. We attempted to mitigate the effect of this potential bias even though we recognize that residual confounding could exist. We took several steps to avoid and evaluate for the possible effect of confounding by indication because the population of patients who received statins might be different from the population that did not in ways that are not related to HCC. First, we examined the effect in stratified analyses in patients with and without liver disease. The findings indicated significant risk reduction in both groups but the magnitude of statin-related risk reduction was larger among patients with known liver disease than those without liver disease. Second, we estimated and adjusted the analyses for the propensity to use statins using the propensity score method 22 and found that the adjustment attenuated but did change the direction or remove the significance of the observed inverse association between statins and HCC. Third, we conducted an analysis in which statin prescriptions recorded within 1 year preceding HCC were excluded, assuming that in this time period liver disease is likely to be severe and overt; in these analyses, we found the associations between statins and HCC to be less strong in general. These lost significance in the adjusted analysis and in some of the stratified analyses of patients with and without liver disease. However, the number of cases and controls in some of these categories was relatively small. For example, only 55 cases and 606 controls were examined for at least 18 months in patients without liver disease. Lastly, we examined the association between HCC and filled prescriptions of nonstatin cholesterollowering drugs as well as triglyceride-lowering drugs. None of the exposures related to either of these 2 classes was associated significantly with HCC. To account for possible changes in prescription as well as disease management practices, we used sampling on incidence density in which cases and controls are on contemporaneous as well as equal time durations. Although a randomized controlled trial would be the preferable study design to obtain unbiased estimates, conducting such a trial for HCC, although possible, is infeasible because of the small fraction of cases that occur annually. Such a trial also would not be justified without preliminary evidence from observational studies. Apart from the novelty of findings, our study had several strengths including the large sample size, the relatively long period of potential exposure, accurate definitions of the case/control and statin prescription validated by chart reviews, and the close matching between cases and controls. Our choice of conducting a nested case-control study among patients with diabetes was related to the known higher likelihood of developing HCC, and to the higher likelihood of using statins to treat commonly found lipid abnormalities. On the other hand, the study had limitations related to the observational retrospective nature of its design and the reliance on a convenience sample of patients identified in VA Medicare datasets. The relatively short duration of exposure (average, 2.4 y) has limited the duration response analyses; however, the limited exposure period imposed by the convenience sample may not be interpreted as the same as short duration of statin use. It is possible that the short-term patterns of statin use observed within the study frame are reflective of long-term use that was not captured. The accuracy and completeness of potential confounders such as hepatitis C, alcoholic liver disease, and cirrhosis is unclear. These conditions are more likely to be identified and recorded in patients with HCC, and therefore the effect of misclassification is to reduce any observed association between statins and HCC. Approximately one third of HCC cases had none of these risk factors in the VA administrative or Medicare claims data. A likely explanation is the absence of diagnostic codes for nonalcoholic fatty liver disease. Our chart review supports the overall proportion of cases with HCV and alcoholic liver disease reported from administrative datasets but also indicates that nonalcoholic fatty liver disease was found in approximately 38% of cases. Given that all patients in this cohort had established diabetes, one expects nonalcoholic fatty liver disease to be disproportionately high in the study. Statin filled prescriptions were used to approximate actual intake of medications; the adherence to these medications is unknown. However, filled prescriptions correlate highly with self-reported intake of medication in previous studies. 27,28 Lastly, the findings were obtained from a predominantly male veteran population and

8 1608 EL SERAG ET AL GASTROENTEROLOGY Vol. 136, No. 5 therefore the findings may not be generalizable to women or nonveterans. In conclusion, this large, nested, matched, case-control study in patients with diabetes provides the first indication of a cancer-preventive effect for statins specific to HCC. These findings needs to be confirmed in future studies. References 1. Blanco-Colio LM, Villa A, Ortego M, et al. 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, atorvastatin and simvastatin, induce apoptosis of vascular smooth muscle cells by downregulation of Bcl-2 expression and Rho A prenylation. Atherosclerosis 2002;161: Kaye JA, Jick H. Statin use and cancer risk in the General Practice Research Database. Br J Cancer 2004;90: Shibata MA, Kavanaugh C, Shibata E, et al. Comparative effects of lovastatin on mammary and prostate oncogenesis in transgenic mouse models. Carcinogenesis 2003;24: Wong WW, Dimitroulakos J, Minden MD, et al. HMG-CoA reductase inhibitors and the malignant cell: the statin family of drugs as triggers of tumor-specific apoptosis. Leukemia 2002;16: Rao S, Porter DC, Chen X, et al. Lovastatin-mediated G1 arrest is through inhibition of the proteasome, independent of hydroxymethyl glutaryl-coa reductase. Proc Natl Acad SciUSA1999; 96: El-Serag HB, Rudolph KL. Hepatocellular carcinoma: epidemiology and molecular carcinogenesis. Gastroenterology 2007;132: Huether A, Hopfner M, Baradari V, et al. EGFR blockade by cetuximab alone or as combination therapy for growth control of hepatocellular cancer. Biochem Pharmacol 2005;70: Sutter AP, Maaser K, Hopfner M, et al. Cell cycle arrest and apoptosis induction in hepatocellular carcinoma cells by HMG- CoA reductase inhibitors. Synergistic antiproliferative action with ligands of the peripheral benzodiazepine receptor. J Hepatol 2005;43: Taras D, Blanc JF, Rullier A, et al. 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Effect of HMG-CoA reductase inhibitors on proliferation and protein synthesis by rat hepatic stellate cells. J Hepatol 2003;38: Choo PW, Rand CS, Inui TS, et al. Validation of patient reports, automated pharmacy records, and pill counts with electronic monitoring of adherence to antihypertensive therapy. Med Care 1999;37: Steiner JF, Prochazka AV. The assessment of refill compliance using pharmacy records: methods, validity, and applications. J Clin Epidemiol 1997;50: Received June 2, Accepted January 26, Reprint requests Address requests for reprints to: Hashem B. El Serag, MD, MPH, The Michael E. DeBakey Veterans Affairs Medical Center, 2002 Holcombe Boulevard, Houston, Texas hasheme@bcm.tmc.edu; fax: (713) Conflicts of interest The authorsdisclose no conflicts. Funding This research was supported in part by the Department of Veterans Affairs, Health Services Research and Development Service (IIR ), and by a grant from the American College of Gastroenterology. Dr El Serag is supported by a National Institutes of Health grant (K24DK ).