Obesity-associated cancers

RELATED CONDITIONS: Many types of cancer

DEFINITION: Obesity is an increase in body weight through an accumulation of fat in the body such that people exceed their ideal weight (taking into account height, sex, age, and body build) by 20 percent or more. The National Institutes of Health define obesity as a body mass index (BMI) of 30 and above; 40 and above is generally considered severely obese. (A BMI of lower than 18.5 is underweight, 18.5 to 24.9 is healthy, and greater than 25.0 is overweight.) BMI, which relates a person’s height and weight, is calculated by multiplying the person’s weight in pounds by 703, then dividing that number by the person’s height in inches squared.

Another important measurement that relates to obesity is a person’s waist measurement. A non-pregnant woman with a waist measurement of more than 35 inches and a man with a measurement of more than 40 inches are considered to be at higher risk for disease. Even if a person’s BMI falls within a healthy range, the risk of developing health problems is greater if body fat is concentrated mainly in the waist area.

Obesity has long been connected with the risks of developing many disorders, including diabetes, arthritis, stroke, and respiratory and heart disease. Research has shown that obesity has a significant effect on the development of cancer and its prognosis after treatment. According to the International Agency for Research on Cancer, overweight and obesity are associated with thirteen cancers in particular: breast (postmenopausal), colorectal, esophageal (adenocarcinoma), gallbladder, liver, kidney, meningioma, multiple myeloma (a blood cancer), ovarian, pancreatic, stomach, thyroid, and uterine. Further research may find links to other cancers as well.

Risk factors: Obesity is primarily caused by poor diet (excessive intake of calories) and physical inactivity. Weight gain may be caused in part by the abundance of readily available high-calorie food choices and the lack of physical exertion in modern lives, psychological factors such as stress or depression, physical conditions such as hypothyroidism, and certain medications including migraine medications and antidepressants. Research has also shown links between genetics and obesity, demonstrating an inherited predisposition in some people to gain weight more easily or difficulty losing weight.

Etiology and the disease process: Many researchers have studied obesity and its relationship to an increased incidence of certain cancers. It is believed that fat cells in the body produce hormones and other substances that affect cell growth. Obese people have significantly increased levels of these compounds because of the increased number of fat cells, which can have potentially influential effects on cellular growth and planned cellular death (apoptosis), perhaps allowing damaged cells to survive and grow into tumors. The roles of estrogen, insulin, insulin-like growth factor-1 and insulin-like growth factor-binding protein-3, leptin, and cytokines, as well as other substances and growth factors, are being examined for their relationship to obesity-associated cancers.

An example of these actions by fat tissue can be found in postmenopausal breast cancer, which is known to have a higher incidence rate in obese women. Estrogen, which is important for the reproductive cycle, is produced by fat tissue in addition to being produced by the ovaries. After menopause, when the ovaries stop producing hormones, fat tissue becomes the most important estrogen source. In obese women, postmenopausal estrogen levels are 50 to 100 percent higher than in women who are not overweight or obese. As a result, estrogen-sensitive tissues in obese women are overexposed to estrogen stimulation, leading to a more rapid growth of estrogen-receptor-sensitive breast tumors. Researchers believe that the fat cells stimulate surges of hormones, insulin, proteins, and the other substances mentioned above that may, in turn, cause reactions that initiate uncontrollable growth among certain cell types. A 2019 study published in Current Oncology Reports found that treatments for obese breast cancer patients had lower efficacy rates than non-obese patients. It also found that obese breast cancer patients were at increased risk for local recurrence.

Incidence: According to the American Cancer Society, the risk of cancer from obesity is similar to the risk from using tobacco. Obesity has reached epidemic proportions and affects the entire population, regardless of age, gender, race, or ethnicity. In the United States, obesity has been increasing at an alarming rate. In 1980, about 15 percent of adults were classified as obese; by 2011, that number had more than doubled to about 35 percent. According to the US Centers for Disease Control and Prevention (CDC), between 1988–94 and 2011–12, the number of adults classified as severely obese had increased from 2.8 percent to 6.4 percent. A 2013 American Journal of Public Health study found that between 1986 and 2006, overweight and obesity accounted for 5 percent of deaths among African American men, 15.6 percent among white men, 26.8 percent among African American women, and 21.7 percent among white women. According to the CDC, between 2017 and 2020, obesity in the United States had increased to almost 42 percent, with severe obesity rising to over 9 percent.

Childhood obesity has been at the forefront of concern because of the staggering numbers of overweight children and the projected long-term health effects. The National Cancer Institute (NCI) reported in 2017 that between 1988 and 1994, only about 10 percent of American children and youth aged two to nineteen and 56 percent of adults were obese; by 2011–14, 17 percent of children and adolescents were obese, as were 36.5 percent of adults, according to the National Health and Nutrition Examination Survey. Overweight and obesity are most common among black and Hispanic women, with the similar patterns seen for children and adolescents in these groups. According to the CDC, between 2017 and 2020, almost 13 percent of children in the United States between the ages of two and five years old, 21 percent of children six to 11 years old, and twenty-two percent of adolescents between 12 and 19 years old were obese.

Studies have increasingly linked obesity and cancer. Many studies show that the greater the degree of obesity, the stronger the association with cancer. After analyzing data from 2005 to 2014, CDC and NCI scientists found that more than half of cancers in women and about one-quarter in men, or 40 percent of all cancers diagnosed in the country, were linked to overweight and obesity. Graham Colditz, a physician with the Harvard School of Public Health, estimated that 50 to 60 percent of cancer cases could be avoided if no one were overweight or obese.

Symptoms: There are no symptoms that are specific to obesity-associated cancers.

Screening and diagnosis: Screening for obesity-associated cancers includes annual physical examinations to calculate BMI and take waist measurements as well as annual laboratory tests, such as serum lipid panel, fasting glucose level, and thyroid function tests. In addition, people can essentially screen themselves by monitoring their own weights. There are no specific tests for obesity-related cancers; testing is done when patients exhibit other symptoms. Staging is specific to the type of cancer that develops.

Treatment and therapy: Treatment for obesity-associated cancer is specific to the type of cancer. However, based on data obtained during various studies, patients must also reduce their weight to avoid the increased risk that obesity places on successful treatment. Patients must set weight-loss goals and obtain assistance from a registered dietitian or weight-loss program for in-depth counseling. Many reputable commercial and community programs exist for obesity treatment. Desirable programs should include diets that meet the United States recommended daily allowance for nutrients, exercise counseling, behavior modification, and provision for long-term maintenance.

The National Institutes of Health guidelines suggest nonpharmacologic treatment for six months and then consideration of weight-loss medication if weight loss is unsatisfactory in those with a BMI greater than 30 or a BMI greater than 27 with associated risk factors. Patients with severe obesity (BMI greater than 40) may also be considered for gastric bypass or gastroplasty procedures.

Prognosis, prevention, and outcomes: Long-term maintenance of weight loss is extremely difficult. If the patient is not motivated, successful weight loss is unlikely. Obesity can be prevented by educating children and adults in healthy dietary habits and exercise requirements, but only if individuals choose to follow the guidelines and do not have physical causes for the excess weight. Weight reduction can have a significant impact on a person’s risk for developing obesity-associated cancers.

Though research clearly links obesity with the propensity for various cancers, the research that examines mortality rates in obese patients varies. A study published in Innovation in 2022 found that overweight or mildly obese cancer patients had better survival rates than patients with low or normal BMI. The study also found that it was not beneficial for overweight or mildly obese patients to lose weight, especially during treatments. Another study, published by the European Society for Medical Oncology, found that mortality rates in obese cancer patients depended on the type of cancer the person had. For example, obese breast cancer patients had a lower survival rate than non-obese patients, but obesity acted as a protective factor in patients with gastrointestinal tumors. Yet another study, published in Ocular Oncology, noted a link between obesity and a lack of metastases and death in patients with uveal melanoma, demonstrating that the cancer in obese patients was not spreading like it was in non-obese or overweight patients. However, it is important to note that varying research and studies do not, and sometimes cannot, account for causality. Therefore, further research is necessary in order to better understand BMI rates and mortality among cancer patients.

Bibliography

“Adult Obesity Facts.” CDC, 14 May 2024, www.cdc.gov/obesity/php/data-research/adult-obesity-facts.html. Accessed 25 June 2024.

"Body Weight and Cancer Risk." Cancer.org. American Cancer Society, 5 Feb. 2016, www.cancer.org/cancer/cancer-causes/diet-physical-activity/body-weight-and-cancer-risk.html. Accessed 19 Jan. 2018.

Calle, E. E., et al. “Overweight, Obesity, and Mortality from Cancer in a Prospectively Studied Cohort of U.S. Adults.” New England Journal of Medicine 348.17 (2003): 1625–38. Print.

"Cancers Associated with Overweight and Obesity Make Up 40 percent of Cancers Diagnosed in the United States." CDC, US Dept. of Health and Human Services, 3 Oct. 2017, www.cdc.gov/media/releases/2017/p1003-vs-cancer-obesity.html. Accessed 19 Jan. 2018.

Fryar, Cheryl D., et al. Prevalence of Overweight, Obesity, and Extreme Obesity among Adults: United States, Trends 1960–1962 through 2011–2012. National Center for Health Statistics, Centers for Disease Control and Prevention, Sept. 2014, www.cdc.gov/nchs/data/hestat/obesity‗adult‗11‗12/obesity‗adult‗11‗12.pdf. Accessed 19 Jan. 2018.

Giovannucci, E., and D. Michaud. “The Role of Obesity and Related Metabolic Disturbances in Cancers of the Colon, Prostate, and Pancreas.” Gastroenterology 132 (2007): 2208–25. Print.

Lee, Kyuwan, et al. “The Impact of Obesity on Breast Cancer Diagnosis and Treatment.” Current Oncology Reports 21.5 (2019): 41. doi:10.1007/s11912-019-0787-1. Accessed 25 June 2024.

Masters, Ryan K., et al. "The Impact of Obesity on US Mortality Levels: The Importance of Age and Cohort Factors in Population Estimates." American Journal of Public Health 103.10 (2013): 1895–1901. PDF file.

"Obesity and Cancer." Cancer.gov. National Cancer Institute, National Institutes of Health, 17 Jan. 2017, www.cancer.gov/about-cancer/causes-prevention/risk/obesity/obesity-fact-sheet. Accessed 19 Jan. 2018.

Polednak, A. P. “Trends in Incidence Rates for Obesity-Associated Cancers in the U.S.” Cancer Detection and Prevention 27 (2003): 415–21. Print.

Sabazade, S., et al. "Obesity Paradox in Uveal Melanoma: High Body Mass Index Is Associated with Low Metastatic Risk." British Journal of Ophthalmology 108 (2024): 578-587. bjo.bmj.com/content/108/4/578. Accessed 25 June 2024.

Tu, Huakang, et al. “Body Mass Index and Survival after Cancer Diagnosis: A Pan-Cancer Cohort Study of 114 430 Patients with Cancer.” The Innovation 3.6 (2022). doi:10.1016/j.xinn.2022.100344. Accessed 25 June 2024.