Patients who are obese are more likely than are normal-weight patients to present with advanced papillary thyroid cancer and to have an aggressive subtype of the malignancy, according to a report published online May 21 in the Archives of Surgery.
The reasons for these adverse findings are not yet certain, but the findings are enough to warrant more careful screening for thyroid cancer among obese patients, said Dr. Avital Harari of the section of endocrine surgery, University of California, Los Angeles, and her associates.
Increased body mass index has been linked to an increased incidence of thyroid cancer in several study populations. Higher BMI also has been associated with a more advanced stage of disease at diagnosis in several other types of cancer, including breast and prostate cancers.
To assess a possible relationship between obesity and thyroid cancer, Dr. Harari and her colleagues reviewed the medical records of 443 adults who underwent total thyroidectomy as first-line treatment for papillary thyroid cancer and its variants at their institution during 2004-2011.
The study subjects were categorized as normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg), obese (30-39.9 kg), or morbidly obese (at least 40 kg). The age range was 18-93 years, with a mean age of 48 years.
Obese and morbidly obese patients were significantly more likely than were thinner patients to have stage III or IV disease at diagnosis. In addition, for the study cohort as a whole, higher BMI was a significant predictor of presenting with stage III or IV disease, with an odds ratio (OR) of 1.94 for overweight subjects, an OR of 2.11 for obese subjects, and an OR of 3.67 for morbidly obese patients, compared with normal-weight patients.
Subgroup analysis showed that the percentages of the most-aggressive subtypes of papillary thyroid cancer were higher among patients in the obese and morbidly obese categories than they were among those in the normal-weight and overweight categories, the investigators said (Arch. Surg. 2012 [doi:10.1001/archsurg.2012.713]).
It was noteworthy that patients with higher BMI did not have higher complication rates than did thinner patients. Rates of wound infection, excessive bleeding, hypocalcemia, respiratory problems, and reintubations were similar across all BMI categories. "However, the number of patients was underpowered to detect a less than 3% complication rate," Dr. Harari and her associates noted.
Obese and morbidly obese patients were significantly more likely to have laryngeal nerve dysfunction after thyroidectomy – a rate of 12%, compared with a 2.6% rate in overweight patients and a 2.0% rate in normal-weight patients. But that was because the obese and morbidly obese patients already had vocal cord dysfunction at presentation, concordant with their more advanced local disease.
"We believe that the cause of [the] increase in aggressive papillary thyroid cancer in the overweight and obese population could be multifactorial," the researchers said.
One such factor may be that diagnosis is delayed in patients with higher BMI because it is more difficult to palpate thyroid nodules in the obese neck, so tumors are more advanced when they are finally detected. Another possibility is that certain biomarkers common in obesity, such as high leptin levels, are associated with cancer development and progression.
It is also likely that obesity and thyroid cancer are both linked to third biological factor, such as diabetes. A recent study of diet and health in older Americans found an increased risk of papillary thyroid cancer among women with diabetes, Dr. Harari and her colleagues said.
"Given our findings, we believe that obese patients are at a higher risk of developing aggressive thyroid cancers and thus should be screened ... by sonography, which has been shown to be more sensitive in detecting thyroid cancer than physical examination alone," they said.
No potential financial conflicts of interest were reported.