Thyroid cancer is on the rise in the United States and most of that increase is due to papillary thyroid cancer, said Dr. Avital Harari and colleagues at the University of California-Los Angeles David Geffen School of Medicine.

Papillary thyroid cancer accounts for about 80 percent of thyroid cancer cases, according to the U.S. National Cancer Institute.

For the study, the researchers reviewed the medical records of nearly 450 patients with an average age of 48 who had surgery to remove most or all of the thyroid gland as an initial treatment for papillary thyroid cancer or its variations.

The patients were divided into four groups -- normal weight, overweight, obese and morbidly obese -- according to body-mass index, a measure of body fat based on height and weight.

The researchers found that higher body-mass index was associated with more advanced cancer at the time of diagnosis. Obese and morbidly obese patients were more likely to have stage 3 or stage 4 cancer, and obese and morbidly obese patients were more likely to have aggressive forms of the disease.

The study appeared online today in the journal Archives of Surgery.

"Given our findings, we believe that obese patients are at a higher risk of developing aggressive thyroid cancers and thus should be screened for thyroid cancer by sonography, which has been shown to be more sensitive in detecting thyroid cancer than physical examination alone," the researchers concluded in a journal news release.

The findings provide "one more reason to be concerned about the current obesity epidemic -- obese patients have more advanced thyroid cancer," Dr. Quan-Yang Duh, of the University of California-San Francisco, wrote in an accompanying editorial.

"This parallel increase in the rates of obesity and thyroid cancer is intriguing, but without a much larger population study we cannot determine whether obesity causes thyroid cancer," Duh said. "However, the authors found that higher body-mass index is associated with a later stage of thyroid cancer."

"For obese patients with papillary thyroid cancer, the bad news is that the cancer is likely to be more advanced," Duh concluded. "The good news is that thyroid operation remains safe even in obese patients with advanced disease."

More information

The U.S. National Cancer Institute has more about thyroid cancer.