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Am Fam Physician. 2008;77(12):1740-1746

Background: Colorectal cancer and coronary artery disease (CAD) have high prevalences in industrialized nations and concomitant high mortality rates. Recent research has found that these entities are strongly associated, possibly because of shared risk factors (see accompanying table). This study postulates that the metabolic syndrome, comprising many of these risk factors, increases the risks of developing CAD and colorectal cancer. Chan and colleagues attempted to determine the prevalence of colorectal neoplasms in patients with newly diagnosed CAD, as well as which risk factors are shared by these two disease entities.

Diabetes mellitus
High-fat, low-fiber diet
Sedentary lifestyle

The Study: Patients admitted to three Hong Kong hospitals over a two-year period for suspected CAD were considered for participation. Patients with a history of CAD longer than one year, those taking statins or aspirin for more than one year, and those with a history of previously suspected or diagnosed colonic disease were excluded. Patients undergoing coronary angiography were offered colonoscopy. There were two control groups: (1) patients with a negative coronary angiogram, and (2) healthy patients from the general population who did not have angiography, but had a normal upper endoscopy to evaluate functional gastric pain. Participants from all three groups (i.e., CAD-positive patients, CAD-negative patients, and the age- and sex-matched population control) underwent baseline history and laboratory testing.

Results: There were 206 patients in the CAD-positive group, 208 patients in the CAD-negative group, and 207 patients in the matched control group. Colorectal neoplasms were more prevalent in the CAD-positive group than in the other two groups: 34.0 percent of patients in the CAD-positive group had neoplasms, but only 18.8 percent in the CAD-negative group and 20.8 percent in the matched control group. Advanced lesions, defined as cancer or villous adenomas or lesions with high-grade dysplasia or size greater than 1 cm, were present in 18.4 percent of the CAD-positive group, 8.7 percent of the CAD-negative group, and 5.8 percent of the matched control group.

When the two control groups were merged for bivariate regression analysis, the authors found strong evidence of an association between CAD and colorectal neoplasms (odds ratio [OR] = 1.88; 95% confidence interval [CI], 1.25 to 2.70) and advanced colorectal lesions (OR = 2.51; 95% CI, 1.43 to 4.35). Further analysis found that a history of smoking and the metabolic syndrome were independent risk factors in the positive association between CAD and advanced colorectal lesions. The OR for the association between CAD and the metabolic syndrome was 5.99 (95% CI, 1.43 to 28.0). The authors explain that the wide confidence interval occurs because the metabolic syndrome is an amalgam of multiple risk factors and not all of these were found in all patients. Thus, there was a higher OR in patients with all components of the metabolic syndrome, but fewer patients meeting its full definition.

Conclusion: The study found that there was a strong association between CAD and colorectal neoplasms, with a higher prevalence of neoplasms in the CAD-positive group. The metabolic syndrome and a history of smoking were found to be important predisposing factors for both diseases. The authors speculate that inflammation is likely the common pathway in CAD and colorectal neoplasm, accounting for the preventive role of aspirin and, according to one study, possibly that of statins. Insulin resistance also may play a role.

editor's note: The authors mention a possible role for statins in protecting against colorectal cancer, citing their anti-inflammatory mechanism. The protective effect of statins has been a subject of interest in recent years, but the findings are controversial. In contrast to an earlier study that found a 47 percent reduction in colorectal cancer in patients taking statins,1 a case-control study found no significant increase or decrease in the risk of colorectal cancer with statin use, except for an unexplained lower risk of stage IV cancer.2 Another recent population-based cohort study of breast, lung, and colorectal cancers concluded that statins did not confer a clinically significant increased or decreased risk of colorectal cancers.3 By comparison, the findings of the role of nonsteroidal anti-inflammatory agents and aspirin are more robust, but the benefits must be considered in the context of gastrointestinal bleeding.—c.w.

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