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Emulating a target trial in case-control designs: an application to statins and colorectal cancer.

ABSTRACT:

Background

Previous case-control studies have reported a strong association between statin use and lower cancer risk. It is unclear whether this association reflects a benefit of statins or is the result of design decisions that cannot be mapped to a (hypothetical) target trial (that would answer the question of interest).

Methods

We outlined the protocol of a target trial to estimate the effect of statins on colorectal cancer incidence among adults with low-density lipoprotein (LDL) cholesterol below 5 mmol/L. We then emulated the target trial using linked electronic health records of 752 469 eligible UK adults (CALIBER 1999-2016) under both a cohort design and a case-control sampling of the cohort. We used pooled logistic regression to estimate intention-to-treat and per-protocol effects of statins on colorectal cancer, with adjustment for baseline and time-varying risk factors via inverse-probability weighting. Finally, we compared our case-control effect estimates with those obtained using previous case-control procedures.

Results

Over the 6-year follow-up, 3596 individuals developed colorectal cancer. Estimated intention-to-treat and per-protocol hazard ratios were 1.00 (95% confidence interval [CI]: 0.87, 1.16) and 0.90 (95% CI: 0.71, 1.12), respectively. As expected, adequate case-control sampling yielded the same estimates. By contrast, previous case-control analytical approaches yielded estimates that appeared strongly protective (odds ratio 0.57, 95% CI: 0.36, 0.91, for ≥5 vs. <5 years of statin use).

Conclusions

Our study demonstrates how to explicitly emulate a target trial using case-control data to reduce discrepancies between observational and randomized trial evidence. This approach may inform future case-control analyses for comparative effectiveness research.

SUBMITTER: Dickerman BA

PROVIDER: S-EPMC7746409 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSeveral prior studies have found an association between statin use and reduced risk of colorectal cancer. We hypothesized that these findings may be due to systematic bias and examined the independent association of colorectal cancer risk with statin use, serum cholesterol, and change in cholesterol concentration.Methods and findings22,163 colorectal cancer cases and 86,538 matched controls between 1995 and 2013 were identified within The Health Improvement Network (THIN) a population-representative database. Conditional logistic regression models estimated colorectal cancer risk with statin use, serum total cholesterol (mmol/L), and change in total cholesterol level. We confirmed a decreased risk of colorectal cancer with statin use (long-term: odds ratio [OR], 0.95; 95% confidence interval [CI], 0.91-0.99; short-term: OR, 0.92; 95% CI, 0.85-0.99). However, to assess whether the observed association may result from indication bias, a subgroup analysis was conducted among patients prescribed a statin. In this subgroup (n = 5,102 cases, n = 19,032 controls), 3.1% of case subjects and 3.1% of controls discontinued therapy. The risk of colorectal cancer was not significantly different among those who continued statin therapy and those who discontinued (OR, 0.98; 95% CI, 0.79-1.22). Increased serum cholesterol was independently associated with decreased risk of colorectal cancer (OR, 0.89 per mmol/L increase; 95% CI, 0.87-0.91); the association was only present if serum cholesterol was measured near the cancer diagnosis (<6 mo: OR, 0.76; 95% CI, 0.47-0.61; >24 mo: OR, 0.98; 95% CI, 0.93-1.03). Decreases in serum total cholesterol >1 mmol/L ?1 year prior to cancer diagnosis were associated with subsequent colorectal cancer (statin users: OR, 1.25; 95 CI%, 1.03-1.53; nonusers: OR, 2.36; 95 CI%, 1.78-3.12). As an observational study, limitations included incomplete data and residual confounding.ConclusionsAlthough the risk of colorectal cancer was lower in statin users versus nonusers, no difference was observed among those who continued versus discontinued statin therapy, suggesting the potential for indication bias. The association between decreased serum cholesterol and colorectal cancer risk suggests a cholesterol-lowering effect of undiagnosed malignancy. Clinical judgment should be used when considering causes of cholesterol reduction in patients, including those on statin therapy.