The prevalence of obesity has increased substantially in the past in almost all countries of the world, and a further increase is expected for the future. Besides the well-established effects on type 2 diabetes and cardiovascular disease, there is convincing evidence today that obesity also increases the risk of several types of cancer, including colorectal cancer, postmenopausal breast cancer, endometrial cancer, renal cell carcinoma, esophageal adenocarcinoma, pancreatic cancer, and liver cancer. Obesity probably also increases the risk of ovarian cancer, advanced prostate cancer, gallbladder cancer, and gastric cardia cancer. For some cancer types, there is also some evidence that weight gain during adulthood increases cancer risk, e.g., colorectal cancer, postmenopausal breast cancer, endometrial cancer, and liver cancer. However, for most cancers, it is an open question as to whether vulnerability to weight gain in relation to cancer risk depends on specific life periods. There are a number of plausible mechanisms that may explain the relationship between obesity and cancer risk, including pathways related to insulin resistance, inflammation, and sex hormones. For most cancers, there is only limited evidence that weight loss in adulthood decreases cancer risk, which is primarily due to the limited long-term success of weight loss strategies among obese individuals. There is limited evidence suggesting that obesity may also be associated with poor prognosis among patients with colorectal cancer, breast cancer, endometrial cancer, ovarian cancer, and pancreatic cancer. Taken together, these findings support efforts to prevent weight gain on an individual level as well as on a population level. Whether and to what extent overweight or obese cancer patients benefit from weight loss strategies is unclear and needs to be addressed in future studies.
Keywords: Cancer; Disease burden; Epidemiology; Evidence; Mechanisms; Obesity; Prognosis; Risk.