Evidence Brief: Patients with Positive Screening Fecal Occult Blood Tests

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Principal Investigator: Kim Peterson, MS Contributing Investigators: Susan Carson, MPH; Linda Humphrey, MD, MPH; Mark Helfand, MD, MPH, MS Evidence-based Synthesis Program (ESP) Center, Portland VA Medical Center, Portland, OR Washington (DC): Department of Veterans Affairs; April 2013

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Introduction

The American Cancer Society estimates that colorectal cancer (CRC) will be the third most common cause of cancer death for both men and women in the U.S. in 2013. The natural history of the disease suggests that longer delays in CRC diagnosis will negatively influence stage at diagnosis and long-term survival. CRC may be diagnosed by screening asymptomatic patients or by evaluation of symptomatic patients. Previous studies investigating the influence of delays on survival or cancer stage at diagnosis have primarily focused on the evaluation of time from first symptom development in symptomatic patients and have demonstrated inconsistent results. For example, among 13 studies published between 1977 and 2006 included in a 2007 systematic review by Ramos and colleagues, 10 found no association between the symptom-to-diagnosis interval (SDI) and survival and the other three found that increased delays resulted in better chances of survival. As for the relationship between SDI and tumor stage, among 18 studies, 11 found no association, four found that shorter delays were associated with an earlier stage at diagnosis and three paradoxically found that a greater delay was associated with an earlier stage at diagnosis. As noted by Ramos et al., the SDI risk function is likely nonlinear and multifaceted, reflecting a complex interaction between tumor biology and location, the clinical course, patient behavior, and the functioning of the healthcare system, and the studies have varied in their methods for adjusting for these confounding factors. These findings highlight the importance of detecting colorectal cancer through screening, before symptoms appear.

Key questions:

Key Question 1: How does variation in time to colonoscopy affect colorectal cancer-related outcomes in patients referred for diagnostic colonoscopy?

Key Question 2: What are the clinical factors (e.g., reason for referral, positive FOBT or symptoms; type and duration of symptoms; etc.) that moderate the relationship between time to colonoscopy and harm?