Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Environmental and Occupational Health

First Committee Member

Paulo S. Pinheiro

Second Committee Member

Brian Labus

Third Committee Member

Daniel Young

Fourth Committee Member

Timothy Bungum

Number of Pages



Diabetes is a common comorbid condition among colorectal cancer (CRC) patients, yet its effects in CRC outcomes, particularly stage at diagnosis, risk of death and variations by diabetes severity (complications vs no complications) and Hispanic ethnicity have not been adequately studied. The purpose of this study was to investigate the association between pre-existing T2DM and advanced stage at diagnosis in elderly patients with CRC; to examine whether diabetes is an independent predictor of poor survival from all-cause and CRC-specific mortality; to assess whether variations exist by diabetes severity and to analyze the outcomes for the Hispanic group.

The Surveillance Epidemiology and End Results (SEER)-Medicare linked datasets were used to extract data on Medicare beneficiaries 67 years and older residing in the SEER areas who were diagnosed with CRC between 2002 and 2011. These datasets provided clinical, demographic, administrative claims and enrollment information for the Medicare population under study. Pre-existing T2DM was ascertained from the Medicare inpatient and outpatient claims using validated algorithms.

The association of advanced stage at diagnosis with CRC was compared between pre-diabetic and non-diabetic patients using logistic regression. All-cause and CRC cause-specific death risk differences were compared using Cox proportional hazards model and hazard ratios were compared in relation to prior T2DM diagnosis and diabetes severity status. All models were adjusted for relevant factors including demographic characteristics such as age, sex, marital status, race/ethnicity and census poverty level. Clinical factors adjusted for included comorbidity score, grade, histology, stage at diagnosis, year of diagnosis and cancer registry.

The analyses included 93,710 CRC patients. Among the study population, 22,155 (24%) had diabetes prior to CRC diagnosis and, of these, 17% had diabetes-related complications (neuropathy, nephropathy, retinopathy or peripheral circulatory disorders). Diabetic patients were more likely to be older, male, non-White, lived in medium to high poverty level areas, had at least one or more comorbidities, and had tumors in the proximal colon. From the regression models, diabetes was not significantly associated with CRC advanced stage at diagnosis (odds ratio (OR) = 0.986; 95% confidence interval (CI) = 0.953-1.02 for diabetes without complications and OR = 0.963; 95% CI = 0.897-1.034 for diabetes with complications). Similar results were observed for Hispanic patients. Overall mortality was significantly higher among diabetic patients compared to non-diabetic patients (hazard ratio (HR) = 1.198; 95% CI = 1.169-1.228). The results were more pronounced for diabetes with complications (HR = 1.467; 95% CI = 1.339-1.538). Patients who had diabetes with complications were 16% more likely to die of colorectal cancer compared to patients without diabetes in the fully adjust model (HR = 1.162; 95% CI = 1.083-1.247). Among Hispanics, diabetes was an independent predictor of poor survival from all-cause mortality but not CRC specific of death.

This study used population-based data and the findings indicate that pre-existing diabetes contributes to poorer overall survival in patients with colorectal cancer and increased mortality from CRC in diabetes with complications. Because these diseases are more prevalent among the elderly, this group is more likely to have both diseases at the same time and more clinicians will need to develop care plans that are interdisciplinary and take into consideration the added burden of diabetes among CRC patients.


Cancer; Colorectal cancer; Diabetes; Medicare; SEER; Survival


Biostatistics | Epidemiology | Public Health

File Format


Degree Grantor

University of Nevada, Las Vegas




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