The paper trail linking excess weight to increased cancer risk is long.
As obesity rates climb worldwide, research into the complications associated with diagnosing and treating cancer in this portion of the population is becoming more prevalent.
Some of the findings are self-evident: Due to body-image issues and other psychosocial concerns, for example, obese women are less likely to get Pap smears and other invasive tests that may detect gynecologic cancers.
Other data present a more confounding picture. Many obese patients seek treatment for cardiovascular disease, diabetes or other conditions that arise from being overweight. In some cases, their relationship with the health care system gives clinicians an opportunity to diagnose — and treat — cancer in a timely manner. Other times, the health concerns that necessitated the initial visit require so much attention, cancer may go undetected.
Obesity rates — the percentage of people with a BMI of 30 or greater — have doubled worldwide since 1980, with an estimated 9.8% of men and 13.8% of women meeting that criteria, according to research published last year in The Lancet. Now, nearly one-third of Americans are obese, and if trends continue, half of the US population could be classified as such by 2030.
Endocrine Today spoke with several physicians and researchers about the extent to which these populations are screened for cancers, challenges related to surgical options and chemotherapy dosing, the increased risk for drug interactions among those who are taking medications to control other diseases, and obstacles to effective post-treatment care.
“Perhaps the most basic challenge is determining what is overweight or obese,” said Heather Bittner Fagan, MD, FAAFP, MPH, associate professor at Thomas Jefferson University and director of health services research in the department of family and community medicine at Christiana Care Health System. “Given how heavy people in the United States are, it is difficult to know where to draw the line. This may also impact the direction of the research and the outcomes we see. Many of the data are still inconclusive.”
Fagan and colleagues recently published a review paper in the Journal of Obesity that examined the association between weight and cancer screening, while also examining screening rates across race/ethnicity and gender.
Among the findings:
- Obesity is associated with higher rates of prostate cancer screening among all races.
- Obesity is associated with lower rates of cervical cancer screening, particularly among white women.
- No correlation appeared between weight and mammography use in women.
- Obese women were less likely to be screened for colorectal cancer, while the relationship between weight and colorectal screening in men was inconsistent.
Heather Bittner Fagan
“It is striking how variable the relationship between obesity and screening can be,” Fagan said. “There are big differences based on the type of screening and the type of cancer.”
More clinical barriers to screening overweight women for certain cancers may exist.
“Many severely obese women need special accommodations such as larger examination tables, but even with these in place, it may be difficult to examine all the reproductive organs satisfactorily,” Bryan C. Bordeaux, DO, MPH, of the division of general internal medicine at Johns Hopkins University School of Medicine, and colleagues wrote in a review paper in the Cleveland Clinic Journal of Medicine. “Clinical breast examinations may be less reliable because increased tissue volume may make some tumors difficult to palpate.”
The results of Fagan’s paper indicated that fewer body image-based effects were seen in men than in women, but that screening men also can be complex.
Most data indicate that obese men are less likely than nonobese men to undergo a digital rectal exam to screen for prostate cancer. However, because prostate cancer can be detected by a much less invasive blood test, obese men are being screened.
“In prostate cancer, obesity can actually facilitate screening,” Fagan said. “Obese men are already in the [health care] system for other things and are therefore likely to get tested.”
The data is far less consistent for colorectal cancer screening, the only test recommended for both men and women.
Two studies Fagan and colleagues examined indicated obese men had lower colorectal cancer screening rates. One study indicated a higher rate among obese men, and three studies found no association. Four of six studies that examined the same factors in women demonstrated a negative association between obesity and colorectal cancer screening.
“The take-home message is that specialists need to understand obese populations have a patchier history of being screened,” Fagan said.
Obesity has unique results on imaging, said Munir Ghesani, MD, attending radiologist at St. Luke’s-Roosevelt Hospital Center and Beth Israel Medical Center.
“There are essentially two things to look at,” Ghesani said. “How does obesity impact image quality, and (for studies involving ionizing radiation) how does it impact radiation exposure?”
The quality of the image depends on the type of scan.
“Fat in areas like the abdomen can provide better image contrast and actually be helpful in reviewing a CT scan,” he said. “However, if you are doing a nuclear scan, you can get more severe attenuation artifacts in obese patients, and the image quality suffers. Consequently, the quality of PET and nuclear scan images is usually poorer in obese patients.”
To achieve similar image quality, radiation doses may be higher in overweight or obese patients. Increased radiation exposure may, in turn, be linked to increased risk for other cancers.
“That said, the advantage of most current-generation machines is that they are able to adapt to different-sized patients,” Ghesani said.
Socioeconomic factors can also be barriers to imaging.
Obesity is more common in poorer people who are more likely to be uninsured and may be less likely to follow through with expensive procedures, according to Bordeaux and colleagues.
There also are clinical obstacles to imaging in overweight patients.
“Unfortunately, many of our imaging machines are not designed to handle people who are morbidly obese,” Bordeaux told Endocrine Today. “Sometimes, the tables on which patients rest during the procedure cannot safely support the patient’s weight, they might be too narrow to prevent them from falling, or the machine openings are too narrow (in the case of a CT or MRI machine) to allow a patient to pass through to the sensors.”
In some cases, patients must be transported to veterinary hospitals so larger imaging machines can be used, Bordeaux said.