I came across an interesting article in the Journal of the Royal Society of Medicine (March 2014). Caroline Yao et al discussed the subject of Colorectal cancer and Type II diabetes mellitus. It was a study based entirely through literature search. Although the paper touched on various topics and risks associated with diabetes mellitus, particularly when they are subjected to surgery the main message here was: Colorectal cancer is associated with diabetes mellitus.
The authors indicated that some of the studies that they looked at showed that type II diabetes increases the life time risk of colorectal cancer by up to 3 times the risk to the gen population. The exact mechanism by which diabetes increases the risk of colorectal cancer appeared complex and was not very clear. Older patients had a greater risk and poor glycaemic control was also associated with a greater risk. One study demonstrated that patients with HbA1c > than 5% had a 4 fold risk of developing the cancer.
There have been studies that suggest that insulin may increase the risk of colorectal cancer in diabetic patients. The increased risk is abolished if they were also on metformin. Metformin may have antineoplastic properties and patients receiving metformin survive better than type II diabetics who are not on metformin.
They concluded that diabetic patients often presented with diarrhoea and we must not assume that diarrhoea in a diabetic patient is due to diabetes alone. The possibility of colorectal cancer in a patient with diabetes should always be prevalent in a clinician’s mind.
(This topic is also posted in Gasteroenterology)