THURSDAY, Oct. 10 (HealthDay News) -- Better detection alone doesn't explain the dramatic increase in thyroid cancer cases seen in the United States over the past three decades, a new study says.

Researchers who looked at records for more than 200 patients were unable to show that advances in screening are behind the jump in thyroid cancer cases as some specialists believe.

"The incidence of thyroid cancer is on the rise and has nearly tripled in the last 30 years," said lead researcher Dr. David Goldenberg, director of head and neck surgery at Penn State Hershey Cancer Institute.

"Some researchers have attributed this increase in incidence to improved sensitivity of diagnostic techniques," he said, referring to the discovery of small insignificant thyroid cancers via state-of-the-art imaging. "Others do not agree and say that there is a real rise in this disease."

Many thyroid cancers are discovered incidentally when a patient undergoes a diagnostic study for some other reason, such as trauma, neck pain or to detect clogged arteries in the neck, Goldenberg explained.

To try to determine whether the increase in thyroid cancer was due to better diagnosis or more actual cancer, Goldenberg's team compared incidentally discovered versus non-incidentally discovered thyroid cancers to see if the groups had different characteristics.

"We found that patients with incidentally discovered thyroid cancers were older, had more advanced disease and were more likely to be men," he said. "These findings imply that improved detection may not be the only cause for the increased incidence of thyroid cancer."

One expert who was not involved with the study said that the findings -- published online Oct. 10 in JAMA Otolaryngology Head & Neck Surgery -- add to the evidence that thyroid cancer really is on the rise.

"This study suggests that there is an actual true increase in the incidence of thyroid cancer," said Dr. Douglas Frank, director of the center for head and neck surgical oncology at Long Island Jewish Medical Center in New Hyde Park, N.Y. Although this rise is not supported directly by this study, he said, it is felt to be true generally and is supported by other current reports.