Obesity has overtaken smoking as the leading preventable cause of cancer. Among patients diagnosed with cancer, obesity has been linked to poor prognosis.
Melissa A. Kalarchian, PhD
Melissa A. Kalarchian, PhD
Melissa Kalarchian is associate dean for Research and Professor at the Duquesne University School of Nursing in Pittsburgh, Pennsylvania.
Obesity, defined as excess adiposity, is a chronic disease affecting more than 1 in 3 adults in the United States.1 It affects some groups more than others, including women, older adults, an individuals from certain racial/ethnic minority groups. Obesity increases the risk for cardiovascular disease, type 2 diabetes, sleep apnea, and even cancer.
In 2003, the American Cancer Society released a landmark study linking obesity to cancer death among US adults.2 Over a decade later, obesity has been associated with the risk for numerous cancers, including endometrial cancer, esophageal adenocarcinoma, gastric cardia cancer, liver cancer, kidney cancer, multiple myeloma, meningioma, pancreatic cancer, colorectal cancer, gallbladder cancer, breast cancer, ovarian cancer, and thyroid cancer.3 Obesity has also been linked to childhood leukemia.4
In 2014, the American Society of Clinical Oncology (ASCO) identified obesity as overtaking smoking as the leading preventable cause of cancer.5 One recent study documented that 3.6% of all new cancer cases worldwide were attributable to excess adiposity.6 This equates to hundreds of thousands of cancer cases that could potentially be avoided —particularly colorectal, pancreatic, and breast cancer.
The mechanisms underlying the relationship between cancer and obesity are not fully understood. These mechanisms may include insulin resistance and chronic hyperinsulinemia, increased bioavailability of steroid hormones, and localized inflammation.7 More recent data suggest that microbes that live in the gastrointestinal tract may also play a role. A better understanding of these pathways may lead to the development of targeted interventions.
The Obesity Society recommends that adults and children maintain reasonable weight for their height and age for multiple health benefits, including decreasing their risk of cancer.8 Lifestyle modification, including diet and exercise, is the foundation for weight management. However, caloric restriction may lead to biological adaptations which undermine the long-term effectiveness of lifestyle modification.9
Indeed, results of behavioral treatment of obesity have been relatively modest, and maintenance of weight loss is challenging. Adjunct interventions include pharmacotherapy and bariatric surgery. Nonetheless, many providers do not address obesity due to barriers such as lack of information about treatment options, as well as limited time and resources.
Bariatric surgery, recommended for individuals with clinically severe obesity, has been associated with the greatest weight loss and maintenance. A meta-analysis showed that bariatric surgery reduced cancer risk and mortality in formerly obese patients, particularly women.10 However, more research is needed before definitive conclusions can be drawn.
Among patients diagnosed with cancer, obesity has been linked to poor prognosis including surgical complications, cancer recurrence, and even cancer mortality.8 Additionally, cancer treatment can contribute to excess adiposity. Chemotherapy and steroid medication are often associated with weight gain among patients. Causes for treatment-related weight gain may include changes in appetite, reduced activity, fluid retention, or other factors.
Evidence-based interventions to support adoption of a healthier lifestyle among patients with cancer are limited. Weight loss interventions for women with breast cancer have been shown to feasible and safe11 with beneficial effects on body weight and cancer biomarkers.12 More work is needed to develop and evaluate weight management interventions to meet the unique needs of different groups of patients.
The ASCO Obesity Initiative has identified priority areas related to obesity and cancer, raised awareness, and distributed toolkits for patients and providers.13,14 Current efforts are focused on collaborating with groups working on obesity-related initiatives, both within and outside of the field of cancer.
Weight management is important for the general poulation and for patients with cancer. Ongoing interdisciplinary care is key to optimizing health and well-being for all patients.