June 1st 2005
Overweight and obesity increase the risk of developing several cancers.Once cancer develops, individuals may be at increased risk of recurrenceand poorer survival if they are overweight or obese. A statisticallysignificant association between overweight or obesity and breast cancerrecurrence or survival has been observed in the majority of populationbasedcase series; however, adiposity has been shown to have less of aneffect on prognosis in the clinical trial setting. Weight gain after breastcancer diagnosis may also be associated with decreased prognosis. Newevidence suggests that overweight/obesity vs normal weight may increasethe risk of poor prognosis among resected colon cancer patients and therisk of chemical recurrence in prostate cancer patients. Furthermore, obesecancer patients are at increased risk for developing problems followingsurgery, including wound complication, lymphedema, second cancers,and the chronic diseases affecting obese individuals without cancer suchas cardiovascular disease and diabetes. Mechanisms proposed to explainthe association between obesity and reduced prognosis include adiposetissue-induced increased concentrations of estrogens and testosterone,insulin, bioavailable insulin-like growth factors, leptin, and cytokines.Additional proposed mechanisms include reduced immune functioning,chemotherapy dosing, and differences in diet and physical activityin obese and nonobese patients. There have been no randomized clinicaltrials testing the effect of weight loss on recurrence or survival inoverweight or obese cancer patients, however. In the absence of clinicaltrial data, normal weight, overweight, and obese patients should beadvised to avoid weight gain through the cancer treatment process. Inaddition, weight loss is probably safe, and perhaps helpful, for overweightand obese cancer survivors who are otherwise healthy.