Are colonoscopy and sigmoidoscopy effective in reducing the mortality and incidence of colorectal cancer in colorectal cancer screening?

Abstract

BACKGROUND: Colorectal cancer is usually asymptomatic until later stage and the 5-year survival for stage III or IV are 68% and 10 % because of delayed diagnosis. Worldwide, it is the 4th leading cause of death among cancers which accounted for 694,000 deaths in 2012. While healthy diet and lifestyle helps prevent colorectal cancer, increased surveillance through screening has been suggested to attribute to the decreasing trend of colorectal cancer incidence in the United States in the past decade. Identifying what type of colorectal cancer screening methods is more effective is of public health relevance to Hong Kong where colorectal cancer ranks the top leading cancer.

OBJECTIVES: To conduct a systematically review on current literatures to examine whether endoscopy screening by flexible sigmoidoscopy or colonoscopy is more effective for reducing the mortality and incidence of colorectal cancer than no screening as many colorectal cancers arise from adenomatous polyps, which polypectomy is hypothesized to be protective. Meanwhile, different countries adopt different kinds of colorectal cancer screening modalities, but yet, there is no agreement for the types of screening.

METHODS: Four databases, Medline (OVIDSP), Pubmed, CINAHL plus (EBSCOhost), Embase (OVIDSP) were used to search for published journals. Reference list of the identified articles were screened for more relevant studies.

RESULTS: A total of 8 studies were included in this systematic review. There were only 2 randomized controlled trials (RCTs) on screening for colorectal cancer using flexible sigmoidoscopy in asymptomatic and average-risk people and no RCT was found for colonoscopy. Based on the studies reviewed, findings were inconsistent on whether endoscopy screening is more effective in reducing overall colorectal cancer incidence and mortality than no screening. Endoscopy screening, either sigmoidoscopy or colonoscopy was associated with lower incidence of distal colorectal cancer.

CONCLUSION: Screening by flexible sigmoidoscopy or colonoscopy is not clearly associated with lower overall colorectal cancer risks based on current systematic review. Randomized controlled trials or retrospective cohorts are required to clarify the effectiveness of endoscopy screening before considering the implementation of population-wide colorectal cancer screening.