S1136 A New Blood-Based Screening Test for Colorectal Cancer: A Pilot Study

Abstract

Background: Colonoscopy is considered to be the standard of care for the diagnosis of colorectal cancer. However, population-based studies have reported a subset of patients with cancer who do not undergo colonoscopy. The purpose of this study was to estimate the prevalence and identify the predictors of not having a colonoscopy in the period preceding colorectal cancer diagnosis. Methods: Using the population-based SEER registries, we identified patients aged >= 69 with colorectal cancer diagnosed from 1994-2005. Linked inpatient and outpatientMedicare claimswere used to identify receipt of colonoscopy prior to diagnosis. We divided this group into patients who had did not have colonoscopy within 3 years of diagnosis (Group I) and those who had 1 or more colonoscopies from 6 months prior to 30 days after diagnosis (Group II). Patient, sociodemographic and tumor factors were used to identify predictors of not having colonoscopy in univariate and multivariable logistic regression analysis. Results: We identified 79,032 patients, including 19.6% in Group I and 80.4% in Group II. Among patients in Group I, 31.6% had barium enema, 21.4% had flexible sigmoidoscopy and 57.3% underwent CT scan within 6 months prior to and 30 days after diagnosis. Independent predictors of Group I included age > 85, African American race, non-married, nursing home residence, rural residence, lower comorbidity score, diagnosis before 2000, AJCC Stage II-IV, left sided or rectal tumor site, and emergency presentation. Patients without colonoscopy were also less likely to undergo surgical resection (OR 0.55, CI 0.52-0.59). In a Cox proportional hazards model that adjusted for demographics, stage and treatment, not undergoing colonoscopy was associated with a higher risk of death (HR 1.31, CI 1.28-1.33). Conclusions: In this large, population based analysis, almost 20% of newly diagnosed colorectal cancer patients did not undergo colonoscopy at the time of diagnosis. Although these patients were more likely to be elderly with advanced disease, lack of colonoscopy appears to be an indicator of emergency presentation, less aggressive treatment and poorer prognosis.