In one study, the risk for colorectal cancer was shown to be obesity’s molecular and metabolic effects on insulin, IGF-1, leptin, adipocytokines, and sex hormones. When obese men were compared with normal weight men, they had a higher rate of colorectal cancer. However, the rate between rectal cancer and obesity was somewhat lower in comparison with colon cancer and obesity. In women, the association between obesity and colon cancer was less than that in men and there was no appreciable risk of rectal cancer in obese women. In a number of studies, obesity was shown to be a risk factor for more aggressive forms of colon cancer. Additionally, obese patients had lower survival rates and higher cancer recurrence rates. 1
Insulin is suspected to be the best biochemical mediator between obesity and colon cancer. Not all fat is equal. Visceral abdominal fat has been shown to especially play a role. To determine colon cancer risk, it has been proposed that it is important to measure waist circumference as well as BMI. A diet rich in refined sugars and low in fiber has often been shown to increase colon cancer risk. The mechanism is now seen to be because of the hyperinsulinemia that it causes. Increased serum insulin levels lower insulin-like growth factor binding protein 1 levels, and later to increased insulin free IGF-1 levels. IGF-1 is associated with both percentage of body fat and waist circumference (WC). This is why WC may prove to be a better predictor of colon cancer risk. Additionally, IGF-1 is procarcinogenic, it decreases cell death and increases cell growth. It is also know to play a role in the development, progression and metastatic potential of colon cancer. Insulin alone stimulates the growth of colon cancer cell lines. 2
A multitude of retrospective studies looked at margin positivity, rates of recurrence, and survival after resection in those with colorectal cancer and obesity. Dignam et al examined a cohort of 4,288 patients who underwent resection of Duke B/C colon carcinoma and were randomized to participation in different National Surgical Adjuvant Breast and Bowel Project (NSABP) adjuvant chemotherapy trials. It looked at patients over an average of 11.2 years. Overall mortality was increased in those with BMIs equal to or greater than 35. The increase in non-cancer risk did not appear to be significant. However, the cancer related mortality increased by 36%. There was no difference seen between men and women. Many other studies showed similar results. 3
Here, we see the complex role that obesity plays in the development of cancer, this time colorectal cancer. It again confirms the importance of helping our patients understand the profound risks obesity holds. Healthy diet and activity remain the cornerstone in treatment.
1-Clin Colon Rectal Surg. 2011 Dec; 24(4): 229–243.
2- Gut. 2006 Feb; 55(2): 285–291.
3- Clin Colon Rectal Surg. 2011 Dec; 24(4): 229–243.
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