Purpose: The growing number of colorectal cancer (CRC) survivors often have multiple chronic conditions. Comparing nonmetastatic CRC survivors and matched noncancer controls, our objectives were to determine the odds of CRC survivors being diagnosed with cardiovascular disease (CVD)-related chronic conditions and their likelihood of control during the year after CRC diagnosis.
Patients and methods: We retrospectively identified patients diagnosed with nonmetastatic CRC in the Veterans Affairs health care system from fiscal years 2009 to 2012 and matched each with up to 3 noncancer control patients. We used logistic regression to assess differences in the likelihood of being diagnosed with CVD-related chronic conditions and control between nonmetastatic CRC survivors and noncancer controls.
Results: We identified 9,758 nonmetastatic CRC patients and matched them to 29,066 noncancer controls. At baseline, 69.4% of CRC survivors and their matched controls were diagnosed with hypertension, 52.4% with hyperlipidemia, and 36.7% with diabetes. Compared to matched noncancer controls, CRC survivors had 57% higher odds of being diagnosed with hypertension (OR=1.57, 95% CI=1.49–1.64) and 7% higher odds of controlled blood pressure (OR=1.07, 95% CI 1.02, 1.13) in the subsequent year. Compared to matched noncancer control patients, CRC survivors had half the odds of being diagnosed with hyperlipidemia (OR=0.50, 95% CI=0.48–0.52) and lower odds of low-density lipoprotein (LDL) control (OR 0.88, 95% CI 0.81–0.94). There were no significant differences between groups for diabetes diagnoses or control.
Conclusion: Compared to noncancer controls, nonmetastatic CRC survivors have 1) greater likelihood of being diagnosed with hypertension and worse blood pressure control in the year following diagnosis; 2) lower likelihood of being diagnosed with hyperlipidemia or LDL control; and 3) comparable diabetes diagnoses and control. There may be a need for hypertension control interventions targeting cancer survivors.
Keywords: Veterans Affairs, colorectal neoplasms, cancer survivors, cardiovascular disease, comorbidity, chronic disease management
Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the US as well as users of the Veterans Affairs (VA) health care system.1–4 CRC survival rates are improving, resulting in a large population of CRC survivors.5,6 There are an estimated 750,000 living CRC survivors in the US.7 With this increased survivability of CRC, many CRC survivors must also focus on and manage other chronic conditions.
In addition to their CRC, many survivors are also diagnosed with multiple chronic conditions.8 For cardiovascular disease (CVD), the presence of CVD-related chronic conditions may be partially attributed to shared risk factors such as obesity, physical inactivity, diet, and other lifestyle behaviors.9–12 When combined, these behavioral factors may synergistically impact health.13
Among CRC survivors, CVD is a leading cause of death.14–16 Emerging evidence suggests that CRC survivors may be more likely to develop diabetes in the five years following their cancer diagnosis.17However, there is a paucity of research about control of CVD-related chronic conditions among CRC survivors. Understanding the control of CVD-related chronic conditions following CRC diagnosis is critical to ensure survivors’ optimal health.
The VA is a national, high-volume provider of CRC care, and the prevalence of CVD is high among veterans.3 Thus, we compared VA nonmetastatic CRC survivors and matched noncancer controls to accomplish two objectives: (1) determine the odds of nonmetastatic CRC survivors being diagnosed with CVD-related chronic conditions (eg, hypertension, diabetes, hyperlipidemia) and (2) determine their likelihood of CVD-related chronic condition control, each over 12 months following CRC diagnosis or identification.
PATIENTS AND METHODS
This is a retrospective, matched case–control cohort study that was approved by Durham VA Health Care System Institutional Review Board (IRB). The study data contained personally identifiable health information. The IRB granted a waiver of informed consent and HIPAA authorization. The waiver was granted because these analyses used existing, retrospective data originating from the electronic health record and it would not be feasible to recontact every patient, many of whom were deceased.
Nonmetastatic CRC survivor case eligibility criteria
Nonmetastatic CRC survivors were identified from the VA Central Cancer Registry (VACCR), a database capturing information on cancer cases diagnosed and/or treated at any VA facility nationwide.3,18 We identified patients diagnosed with CRC at any VA hospital nationwide from fiscal years 2009 to 2012 (ie, October 1, 2008, through September 30, 2012). To be eligible, CRC survivors must have been newly diagnosed with invasive, stages I, II, or III) at a VA facility during the study time frame and have had at least one primary care or oncology visit in the year prior to their CRC diagnosis. Nonmetastatic CRC survivors were excluded if we were unable to link their VACCR record with VA administrative data sources, had insufficient data to construct covariates, or were not matched with a noncancer control patient (Figure 1).
Noncancer control eligibility criteria
Potential noncancer control patients were identified through VA electronic health record (EHR) data via the VA Informatics and Computing Infrastructure.19 To match nonmetastatic CRC survivors and noncancer control patients, we used sequential stratification exact matching.20,21 This technique allowed for multiple anchor dates and time-varying characteristics, for example, longitudinal variation in body mass index (BMI). These time-varying characteristics may affect patterns of health care utilization and diagnoses with CVD-related chronic conditions (eg, more frequent interaction with health care system leads to more opportunities to be diagnosed), so properly accounting for them via a longitudinal matching process that allowed for these characteristics changing over time was critical. In order to be eligible to match to a nonmetastatic CRC survivor, potential noncancer controls could have no history of any cancer from five years prior until that CRC survivor’s diagnosis date and must have had one or more primary care visits in the previous six months. We chose five years as a threshold because evidence suggests that a pattern of stability emerges by that time.22
Case–control matching process
Nonmetastatic CRC survivors and noncancer control patients were first exact matched on the following characteristics: sex; race (white, non-white); age (within 5 years of the age of the matched case at time of diagnosis), copayment status (no copayment because of disability, no copayment because of low-income, must pay); Veterans Integrated Service Network geographic area; distance to VA healthcare; and health care use (high users [≥3 outpatient visits in the 14 months to 2 months prior to their CRC diagnosis], low users [<3 outpatient visits in the same period]). We used the period from 14 months to 2 months prior to their CRC diagnosis to avoid measuring a temporary increase in health services use related to obtaining a CRC diagnosis. CRC cases and noncancer control patients were matched on three BMI categories (underweight or healthy [BMI<24.9], overweight [25≤BMI≤29.9]), and obesity [BMI≥30.0] using the closest BMI to the case’s diagnosis date between 2 and 14 months prior to diagnosis (1 year for controls). Because CRC patients may experience weight changes around the time of diagnosis that might influence BMI, we excluded measurements within the 2 months prior to diagnosis. Additionally, CRC survivors and noncancer control patients were matched on the presence of CVD-related chronic conditions (hypertension, hyperlipidemia, diabetes diagnoses) between 2 and 26 months prior to the CRC survivor’s diagnosis date (2 years for controls).
After exact matching on the above characteristics, matching was further refined by selecting control patients closest to each CRC survivor based on minimizing the Mahalanobis distance function23including the continuous variables of age and distance to VA health care. Based on the smallest variance that enabled the balance of covariates while minimizing the loss of potential controls, up to three matches were selected for each CRC survivor. An anchor date was established for all patients. For CRC cases, the date of CRC diagnosis was the anchor date. For matched, noncancer controls, the anchor date was the closest primary care visit date that occurred prior to and within six months of the corresponding CRC case’s diagnosis date.
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