Dear Editor,
We would like to thank Dr. Lazzati for the clarification regarding association between bariatric surgery and cancer events in the Swedish Obese Subjects (SOS) study.1
We agree that there are controversial results on the association between bariatric surgery and the risk of colorectal cancer (CRC). However, as pointed out in the response by Dr, Lazzati,1 it seems that reports indicating an increased incidence of CRC are authored by the same researchers and all based on estimated risk differences using non-standardized comparative groups derived from retrospective data.2-4
It is true that all the studies from Sweden, including the SOS study that we represent, capture cancer events from the Swedish National Cancer Register, so this is not the reason for the controversy. Instead the controversy most likely arises from important differences with respect to study design and statistical analysesreviewed in 5. The SOS study is a prospective, long-term study with a carefully matched obese control group, and our result that the risk of CRC is not increased after bariatric surgery is in agreement with other international publications on the topic.6, 7
References
Lazzati, A. Author response to: Effect of bariatric surgery on cancer risk: results from an emulated target trial using population-based data. Br J Surg. 2022.
Derogar, M, Hull, MA, Kant, P, Östlund, M, Lu, Y, Lagergren, J. Increased risk of colorectal cancer after obesity surgery. Ann Surg. 2013:258(6):983-8.
Östlund, MP, Lu, Y, Lagergren, J. Risk of obesity-related cancer after obesity surgery in a population-based cohort study. Ann Surg. 2010:252(6):972-6.
Tao, W, Artama, M, von Euler-Chelpin, M, Hull, M, Ljung, R, Lynge, E, Olafsdottir, GH, Pukkala, E, Romundstad, P, Talback, M, Tryggvadottir, L, Lagergren, J. Colon and rectal cancer risk after bariatric surgery in a multicountry Nordic cohort study. Int J Cancer. 2020:147(3):728-735.
Bruno, DS, Berger, NA. Impact of bariatric surgery on cancer risk reduction. Ann Transl Med. 2020:8(Suppl 1):S13.
Bailly, L, Fabre, R, Pradier, C, Iannelli, A. Colorectal Cancer Risk Following Bariatric Surgery in a Nationwide Study of French Individuals With Obesity. JAMA Surg. 2020:155(5):395-402.
Afshar, S, Kelly, SB, Seymour, K, Lara, J, Woodcock, S, Mathers, JC. The effects of bariatric surgery on colorectal cancer risk: systematic review and meta-analysis. Obes Surg. 2014:24(10):1793-9.
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