Obesity is at a crisis level. In 2014, two-thirds of Americans had a body mass index (BMI) of 25 or greater, meeting the criteria for being either overweight (25-29.9) or obese (30+) (Morb Mortal Wkly Rep 2017;66:1052-1058).
There are numerous documented comorbidities associated with obesity. Cancer may not be top of mind among them, but the connection between obesity and cancer deserves a closer examination.
The CDC reports that being overweight or obese is considered a risk factor for 13 different cancers. Those cancers accounted for 40 percent of all cancers diagnosed in 2014 (Morb Mortal Wkly Rep 2017;66:1052-1058). Obesity is the second largest environmental risk factor for cancer, behind tobacco use (The ASCO Post 2017;8(9):128-129,133-134). Obesity-associated cancers are more common in those over age 50 and non-Hispanic black and white adults (Morb Mortal Wkly Rep 2017;66:1052-1058). If obesity rates continue to climb at existing rates, there will be an estimated half a million additional cases of cancer in the U.S. by 2020, according to the ASCO 2017 National Cancer Opinion Survey.
One of the cancers that obesity contributes to is gastric cardia, or cancer of the upper stomach. Overall, there are approximately 26,370 new cases of this kind of cancer diagnosed annually in the U.S, according to the American Institute for Cancer Research (AICR). And a CDC Vital Signs report on cancer and obesity reveals that people who are overweight or obese are twice as likely as people with a BMI between 18.5 and 24.9 to develop gastric cardia cancer. For every kilogram increase in BMI, there is a 4 percent increased risk of developing gastric cardia cancer (Morb Mortal Wkly Rep 2017;66:1052-1058).
Physiologically, the chronic inflammation associated with obesity increases the risk of gastric cardia cancer. According to the AICR Continuous Update Report on Stomach Cancer, obesity can cause the body to produce more insulin and leptin, which may lead to increased cell proliferation, promoting growth of cancerous cells.
Men are more frequently diagnosed with gastric cardia cancer than women, according to the Vital Signs report. Brooke Steele, DO, Division of Cancer Prevention and Control, CDC, explained the reasons for gender disparity aren't clear. “The differences of type and distribution of adipose tissue in men and women could be a factor. Men and pre-menopausal women store fat in different areas.” Where adipose tissue is stored on the body does make a difference. Steele said that obesity, especially abdominal fat, promotes esophageal reflux, which can be a risk factor.
Nigel Brockton, PhD, Director of Research, AICR, which has published its own research on stomach cancer, said that beyond obesity, smoking, and alcohol consumption, both risk factors for gastric cardia cancer, are behaviors more prevalent in men. Occupation is another potential factor. “There is some evidence that dusty environments, wood processing, industrial chemical exposure, coal mining, and rubber processing can be associated with increased risk of gastric cardia cancer,” noted Brockton.
Some reports, such as the Vital Signs, specify obesity as a risk factor specifically for upper stomach cancer. Alice G Bender, MS, RDN, Director of Nutrition Programs, AICR, cautions that a lot of studies on stomach cancer don't differentiate between types. “This is a feature of the fact that H. pylori is the main driver of non-cardia gastric cancer. It's difficult to tease out the effect of obesity,” said Brockton.
Once patients are diagnosed with gastric cardia cancer, obesity can affect treatment protocols, although Steele admits that research is quite limited. There have been mixed findings in surgery studies for gastric cancer patients, with some reporting longer times spent in surgery. Bender noted that obesity can affect chemotherapy dosage.
It's important to note that gastric cardia cancer is not driven by a single factor. “Obesity layers on top of other factors,” explained Brockton. “Anything you do to reduce your risk of gastric cardia cancer reduces your risk of other cancers.”
Prevention is a large step in the march against cancer. Yet, the public is largely unaware of the cancer-obesity connection. ASCO's National Cancer Opinion Survey taken in July 2017 showed 31 percent of respondents correctly identified obesity as a risk factor for cancer, behind the 78 percent and 66 percent who correctly identified tobacco use and sun exposure as risk factors.
“CDC wants to get the word out that obesity is a risk factor in cancer,” Steele noted. “It will take combined efforts of government and communities to combat it.” The CDC's National Comprehensive Cancer Control Program focuses on promoting physical activity and a healthy diet as a means of lowering cancer risk. The program brings together medical centers, universities, faith-based organizations and non-profits, local and state politicians, public health programs, and other stakeholders into coalitions. Each coalition creates a plan to address risk factors for the most common cancers in their area, a plan can include a focus on maintaining a healthy weight.
Prevention also begins at the individual level. The ASCO National Cancer Opinion Survey showed 41 percent of Americans maintain a healthy weight to decrease their cancer risk and 48 percent exercise on a regular basis.
Oncologists as Guides
With the current obesity rates in America, oncologists will encounter cancer patients who are overweight or obese. How should they approach addressing the disease in this subset of patients?
“Oncologists are very focused on the treatment of the disease and the immediate threat,” Brockton noted.
“There is a lack of focus on behavioral interventions,” Bender added, yet there are good intentions.
There is awareness among Brockton and Bender's oncologist colleagues of the obesity and cancer connection, yet anecdotally, Bender reported there is a lack of conversations with patients. Oncologists, however, believe they should be having more discussions with their patients about the dangers of obesity.
Recognizing this lack of focus and its threat to cancer prevention and treatment, ASCO hosted the Summit on Addressing Obesity through Multidisciplinary Collaboration, bringing together 19 health care associations and academies. The summit recommended increased provider training around obesity, such as developing core competencies and guidelines across the medical spectrum. It also recommends oncologists join with other health care providers to deliver joint messages to the public about the dangers of obesity.
Different specialties researching prevention and treatment options should better share their findings, encouraging collaboration across disciplines (Obesity 2017;25:S34-S39). Conversations with patients are crucial to halting the spread of cancer. Health professionals already talk to obese patients about their elevated risk factors for chronic disease like diabetes and heart disease. They should add cancer to that conversation mix. It's important those discussions don't blame the patient and share actionable steps.
“Doctors should help patients find healthy lifestyle programs that can help them lose weight,” Bender said. Referrals to health professionals experienced in working with people with obesity, such as registered dietitians like herself, are encouraged. Many people are standing by to help patients get on the path to a healthier lifestyle.”
To lower their risk of developing upper stomach cancer, AICR recommends Americans move at least 30 minutes each day; avoid sugary drinks and processed, high fat foods; limit salt intake; and eat more whole grains, fruits, and vegetables. Those are also useful recommendations for maintaining a healthy weight. Better education of both clinicians and the general public will go a long way to raise awareness of the cancer and obesity connection, and hopefully, lower the instances of both diseases.
Danielle Bullen Love is a contributing writer.