Risk of colorectal cancer following adenoma removal – SAR
The increasing use of colonoscopy both for examination of symptomatic and for screening purposes entails detection of a large number of patients with adenomas in the colon and the rectum. The majority of these lesions, widely considered to be precursors of colorectal cancer, can be removed during colonoscopy. There is a wide-spread perception that these individuals are at increased risk of developing new precursors and in the long-term at increased risk of developing also invasive cancer. Based on features of the removed lesion, they are classified – according to different algorithms – into low and high, sometime even intermediate risk lesions and subjected to various follow-up regimen. However, the fundamental challenge is to properly quantify the excess risk of colorectal cancer, if any, following adenoma removal. Based on results from Norway that we published in 2014, this risk might have been exaggerated particularly among patients with low risk adenomas. In order to confirm or refute the findings from Norway, we performed a large-scale study also in Sweden. We enrolled about 50,000 Swedish individuals that had adenomas removed and followed them through record linkages in order to quantify their subsequent risk of colorectal cancer. The study was recently published and confirms the results of the previous Norwegian publication that relative and absolute risk increase compared to standardized incidence-based mortality ratios is marginal. The findings underline the urgent need for improved risk stratification.
We also plan a nested case-control study (cases being patients who develop cancer following adenoma removal and control samples of those who did not develop cancer). In this study, we will retrieve much more detailed information from hospital records and pathology reports in order to improve risk stratification. At present this part of the study is limited to Norway due to lack of funding for the Swedish chart examination.
Participants: Hans-Olov Adami (PI), Louise Emilsson (Project Leader)
Collaborators in Norway: Mette Kalager, Michael Bretthauer, Magnus Løberg
Financing: The Swedish Cancer Society, The Research Council of Norway