Individual-level factors in colorectal cancer screening: a review of the literature on the relation of individual-level health behavior constructs and screening behavior.

Colorectal cancer is a serious contributor to disease morbidity and mortality in the United States and other nations. In 2008 it ranked second in cancer deaths and third in new cancer cases in the United States (1); worldwide mortality is over 600,000 deaths per year (2). Screening for colorectal cancer is a cost-effective prevention and control strategy (3); it leads to earlier detection, which is associated with improved survival (4-9). Unfortunately, only about 1/3 of colorectal cancers are diagnosed at an early stage (10-11). This is due to low rates of screening compliance -- only about 1/2 of US adults are compliant with recommendations for colorectal cancer screening (12) and only 15 states have population screening compliance rates greater than 60% (13). Increasing compliance with colorectal cancer screening recommendations is a critical need for reducing the substantial personal and social costs of colorectal cancer morbidity and mortality (14). Several screening tests are available to detect colorectal cancer and are widely disseminated for use in clinical practice (9, 15-16). There is no single recommended screening test for colorectal cancer, and relative use of each test has changed over time (17). At the time that this literature review was conducted, four screening tests were recommended: fecal occult blood testing (taking fecal samples and placing them on a test card; recommended yearly), flexible sigmoidoscopy (endoscopic procedure that images the lower colon; recommended every five years), colonoscopy (endoscopic procedure with anesthesia that images the entire colon; recommended every ten years), and double-contrast barium enema (x-ray procedure following barium/air enema; recommended every five years)(18-23). Newer recommendations have added other stool-based testing (e.g., stool DNA tests) and newer imaging techniques (e.g., computerized tomography colonography; 24). Studies have been done on a number of demographic, social, and environmental determinants of colorectal cancer screening (e.g., insurance coverage, discussion with a medical professional (25-27)). Given that screening ultimately requires behavioral action on the part of the individual person (e.g., going to a colonoscopy appointment; completing and mailing an FOBT card), understanding factors involved in individual decision making regarding screening is necessary to improve upon suboptimal screening compliance. The health behavior literature includes numerous theoretical models that describe factors serving as inputs to individual behavioral choices about engaging in health-related behaviors (28-30). The importance of theory-based approaches for both understanding health behavior and developing behavior change interventions is frequently discussed (28, 31-33). Previous reviews of the literature on determinants of colorectal cancer screening have included some variables that address individual-level determinants related to engaging in screening tests. However, to our knowledge no previous review has systematically examined the extent to which major theoretical models of individual behavior have been examined in the context of colorectal cancer screening behavior and not all of the constructs commonly examined in such models have been included in past literature reviews. Moreover, the existing reviews are five or more years old. There are, therefore, multiple newer studies that have not previously been reviewed. This is especially true for colonoscopy screening, which was the newest screening test widely used in clinical practice at the time of the last review (25). The key objective for this systematic review is to examine the state of understanding of how individual-level health behavior models have been addressed in the literature on colorectal cancer screening behavior. The purpose is to provide an assessment of what constructs and theoretical models have and have not been studied, to explore the sufficiency of our examination of these constructs in the context of colorectal cancer screening, and to summarize the support found for the role of such constructs as factors associated with colorectal cancer screening behavior. The review focuses on decision-making constructs from four key models: the health belief model (34), the theory of planned behavior (35), social cognitive theory (36), and the transtheoretical model (37). These four were selected because they are collectively widely used in the field (28) and have been applied across a range of health-related contexts. Because many health behavior models share common underlying assumptions, constructs from these four models also collectively provide a fairly comprehensive representation of constructs included in other health behavior models (30, 38). To address these objectives, we conducted a comprehensive search for published empirical studies examining the relation between constructs included in the four models and colorectal cancer screening behavior and/or behavioral intentions. Relevant studies were reviewed and their findings concerning the relation of the constructs and behavioral outcomes were coded. In addition, we examined the relation of a number of methodological, measurement, and population characteristics of the studies to their findings about the relation of constructs and behavioral outcomes.