Excess weight as a risk factor common to many cancer sites: words of caution when interpreting meta-analytic evidence

Excess weight as a risk factor common to many cancer sites: words of caution when interpreting meta-analytic evidence | Cancer Epidemiology, Biomarkers & Prevention

Abstract
 For over a decade, excess body weight, commonly categorized as overweight (body mass index, BMI: 25.0 to 29.9 kg/m2) and obesity (BMI: ≥ 30 kg/m2) has been an established incidence risk factor for several adult cancers (1). For 2012, the burden of disease attributed to elevated BMI was estimated as nearly half-million new cancers worldwide, making this the third highest ranked cancer risk factor globally after smoking and infections (ranked second in most western populations) and an important public health problem (2, 3). In recent years, scientific evidence on BMI-cancer associations has continued to accumulate and reveal positive associations for even more and more cancer sites. Among the most comprehensive and systematic evaluations undertaken on these associations have been through the World Cancer Research Fund (WCRF) continuous update project, which now links excess weight or body fatness to 11 cancers (4).

In 2016, an expert working group of 21 scientists from eight countries, gathered under the auspices of the International Agency for Research on Cancer (IARC), to evaluate the preventive effects of avoidance of excess body fatness on cancer risk. This group extended the list of obesity-related cancers, for which sufficient evidence exists, to thirteen as follows: cancers of the colon and rectum, esophagus (adenocarcinoma), kidney (renal cell), breast (post-menopausal), endometrium, gastric cardia, liver, gallbladder, pancreas, ovary, thyroid, multiple myeloma and meningioma. Considering that excess body adiposity is related to a vast array of metabolic and physiological dysfunctions, underlying biological mechanisms have been identified explaining many of these associations.