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Screening of colorectal cancer (CRC) by sigmoidoscopy or colonoscopy has been shown to reduce incidence and mortality of colorectal cancer. However, it is not clear how screening affects the distribution of colorectal cancer stages at diagnosis. Cancer stage is an important factor that determines the survival of patients diagnosed with colorectal cancer.
For comparison, we can look at stage distribution reported for the general population. Lines et al (2008) reported that for elderly population the fraction of colon cancers diagnosed at stages 0-IV in 1988 was 2%, 19%, 33%, 21%, and 17%, respectively, For rectal cancer, the fractions are 2%, 31%, 24%, 18%, and 15% for Stages 0–4, respectively. It should be noted that in 1988, there was only a very small fraction of people that participated in screening.
Doria-Rose et al. (2004) examined a cohort of 72,483 participants in the Colon Cancer Prevention program of Kaiser Permanente of Northern California (KP). The cohort includes men and women aged 50 years and older who had a negative screening flexible sigmoidoscopy examination between 1994 and 1996. These people were considered not to be at high risk for developing CRC. The cohort was followed for 5 years, during which, 30 cases of distal and 80 cases of proximal CRC occurred, of them, 23% of cancers diagnosed at stage I, 26% of cancers diagnosed at stage II, 21% of cancers diagnosed at stage III and 30% of cancers diagnosed at stage IV.
In the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial, 64 658 subjects (83.5%) underwent screening flexible sigmoidoscopy, and at least one polyp or mass was identified in 15 150 subjects (23.4%). 169 cancers were found. Of them, 58.6% of cancers were diagnosed at stage I, 18.3% at stage II, 14.8% at stage III, and 3% at stage IV.
In an earlier study, Kaye and Shulman (1992) observed a favorable shift in the stage distribution of colorectal cancers diagnosed at HCHP after the FOBT screening program began.
In summary, the evidences seem to suggest that in addition to removal of adenomas (precursors to colorectal cancer) screening increases the probability of colorectal cancers to be diagnosed at early stages.
The incidence of colorectal cancer following a negative screening sigmoidoscopy, VP Doria-Rose, TR Levin, JV Selby, PA Newcomb, KE - Gastroenterology , Volume 127 , Issue 3 , Pages 714 – 722, 2004
Trends in stage distribution and survival among elderly colorectal cancer patients in the U.S., L. M. Lines, K. Lang, D. W. Lee, J. R. Korn, D. J. Vanness, C. C. Earle and J. Menzin Journal of Clinical Oncology, 2008 ASCO Annual Meeting Proceedings (Post-Meeting Edition).Vol 26, No 15S (May 20 Supplement), 2008: 4043