At nearly 11,000 feet, Mount Etna in eastern Sicily is one of the world's most active volcanoes. And while the peak erupts at a slow enough rate for people to escape a lava burial, the gentle giant could put people at an increased risk of a different hazard—the development of thyroid cancer.

Those living in the Catania province, where Mount Etna is located, are 2.3 times as likely as those living in the Mediterranean island's eight other non-volcanic provinces to develop papillary thyroid cancer, which is one the most common forms of thyroid cancer, according to a study published online November 5 in the Journal of the National Cancer Institute. Although thyroid cancer can lead to difficulty swallowing or a hoarse throat, it has one of the highest survival rates—97 percent of patients are still alive five years after diagnosis. Along with the risk factors most commonly associated with this cancer, such as radiation exposure and a diet low in iodine, previous studies have found soaring thyroid cancer rates in the volcanic areas of Hawaii and Iceland.

"The Sicily Island has rural and urban areas…volcanic and nonvolcanic areas, and a homogenous population; thus, Sicily is a favorable setting for the evaluation of environmental influences on thyroid cancer etiology," wrote the authors of the study led by Riccardo Vigneri, a professor of endocrinology at the Garibaldi-Nesima Hospital in Catania.

To parse the relationships among thyroid cancer and different environmental conditions using Sicily as a model, the authors focused on the 1,950 new cases of thyroid cancer diagnosed on the island from 2002 to 2004. Vigneri and his colleagues collected information about the conditions in the region where each patient lived, whether it was volcanic, urban or industrial, or if it was associated with low iodine intake, based on surveys conducted over the past 30 years. In addition, the authors examined the chemical profile of the drinking water in Catania and two nonvolcanic provinces.

These analyses revealed that the greatest number of new thyroid cancer cases were found among people from the volcanic province of Catania. Whereas outside of this province, the average incidence of cases in women and men was 14.1 and 3.0 for every 100,000 residents, respectively, 31.7 women and 6.4 men for every 100,000 were diagnosed with thyroid cancer in Catania between 2002 and 2004. The average overall incidence in Italy of newly diagnosed thyroid cancer among women and men is 15.5 and 5.2 per 100,000 per year, respectively. Although urban areas also had a higher incidence of thyroid cancer than rural areas in this study, the difference was much smaller than that found among volcanic and nonvolcanic provinces.

Clues as to why volcanic activity might be linked to increased risk of thyroid cancer could come from environmental data. As the authors note, the soil under Mount Etna comes into contact with an aquifer that serves more than 750,000 of Catania's approximately one million residents. The neighboring provinces have separate water sources. Previous studies have found that carbon dioxide present in Etna's gas leads to acidification of the water and leaching of elements such as magnesium and boron from the volcanic rock into the water supply. In this study, Vigneri's team found that more of the tap water samples taken from Catania than from the nonvolcanic provinces contained magnesium, boron, iron and vanadium at levels that exceeded those allowed for drinking water.

Another element that could be a culprit for the increased incidence of thyroid cancer is radioactive radon. This element has been associated with high incidences of thyroid cancer following the Chernobyl Nuclear Power Plant explosion in Ukraine. Although the authors did not examine the levels of radon in this study, they have, in previous studies, detected radon at concentrations above the maximum allowed levels in 40 percent of water samples in Catania. With its frequent volcanic activity, Mount Etna spews large amounts of radon into the environment.

Aside from having one of the world's most active volcanoes, the province of Catania shares many features with other regions of Sicily in terms of population, quality of health care and rates of other cancers, such as breast cancer, according to the authors. These similarities suggest that Mount Etna poses a unique thyroid cancer risk, and that "residents of other volcanic areas (many million people worldwide) could be at increased risk," the authors wrote.

Image of Mount Etna courtesy of iStockphoto/ollirg