Diabetes mellitus and colorectal cancer: an evidence-based review

Abstract

Objective: Diabetes mellitus (DM) and colorectal cancer (CRC) are diseases with increasing incidence and high mortality. In 2014, DM accounted for 4.9 million deaths worldwide according to the International Diabetes Federation. Some studies suggest that DM is a risk factor for CRC. However, this association is inconsistent. The aim of this study was to review the evidence for the association between DM and increased incidence and mortality from CRC. Data sources: National Guideline Clearing House, NICE, Canadian Medical Association Practice Guidelines, Cochrane, PubMed, and Direção-Geral da Saúde. Methods: We searched for meta-analyses (MA), systematic reviews (SR), observational studies, and clinical guidelines based on evidence published in the last five years in Portuguese, Spanish and English, using the MeSH terms ‘diabetes mellitus’ and ‘cancer, colorectal’ and the corresponding DeCS (Portuguese search terms). We used the Strength of Recommendation Taxonomy (SORT) scale of the American Academy of Family Physicians to assign levels of evidence and strength of recommendations. Results: From the 48 articles obtained, 6 MA and 1 observational study met the inclusion criteria. Included studies found statistically significant results showing increased mortality and incidence of CRC in diabetic individuals. Four MA conducted an independent analysis by site of cancer (colon and rectum) and found a statistically significant increase in incidence and mortality of both types of cancer in diabetic population. Similarly, four MA conducted a subgroup analysis by gender showing, in most studies, a positive association between diabetes and increased incidence of CRC in both genders. Conclusion: The currently available evidence shows a statistically significant and moderate increase in incidence and mortality from CRC in diabetic individuals (SORT A). We need studies with more homogeneous methodology, regarding subtypes of DM, ethnicity, and the effects of confounding factors such as diet, obesity, smoking, sedentary lifestyle, antidiabetic medication and duration of the disease. These results are clinically relevant and may have public health implications, given the high prevalence and morbidity of DM and CRC and the possible common pathophysiological basis of these diseases.