Under the Shadow of Vesuvius: A Risk for Thyroid Cancer?

Dear Editor:

Thyroid cancer is the most common endocrine cancer (1). The only environmental factors that have been strongly associated with differentiated thyroid cancer (DTC) are iodine deficiency and radiation exposure (2). However, an increased risk of DTC has been reported in some volcanic areas in the world, namely Hawaii, the Philippines, and Iceland (3 –8), and its pathogenesis was attributed to various compounds of the volcanic lava. In Italy, the incidence of DTC was reported to be more than two-fold higher in Catania (Sicily), which is near the volcano Mt. Etna, than in other areas of the island (9).

Our study was prompted by the observation that a large number of patients with DTC attending our hospital were from the area around the volcano Mt. Vesuvius (Campania, Italy). In an attempt to shed light on a possible association between volcanoes and DTC, we retrospectively examined 500 new cases admitted to the University of Federico II of Naples in Campania from 2000 to 2009. Age, sex, tumor size, lymph-node invasion, distant metastases, and cancer histotype were analyzed. We recorded the place of birth and of residence of each patient.

In the attempt to estimate the presence of DTC in the Vesuvius area, we calculated the ratio between the number of new diagnosed PTC cases from the Vesuvius area and the number of residents in the same area. The figures were 9 per 100,000 residents for the papillary histotype and 1.48 per 100,000 residents for the follicular histotype. We then compared this ratio with the same ratio calculated between the number of new PTC cases from the Campania region, excluding the Vesuvius area and the number of its residents, and obtained 6.2 per 100,000 residents for the papillary histotype and 1.12 per 100,000 residents for the follicular histotype. The results confirmed that the number of DTC cases was higher in subjects living in the volcanic area of Vesuvius than in nonvolcanic areas of Campania, which suggests a relationship between DTC and the volcano or environmental factors in this area (Supplementary Data, available online at www.liebertpub.com/thy). As expected, women were more frequently affected, and papillary cancer was the most frequent histotype (Supplementary Data). In addition, the number of cases of the follicular histotype progressively decreased over the years of the study. Moreover, we observed an earlier development of the disease in the Vesuvius area (Supplementary Data). Autoimmune thyroiditis was associated with DTC in 25% of cases.

A previous population-based study did not find an increased risk of thyroid cancer in Campania, where Mt. Vesuvius is located (10). The difference between the latter study and our study could be due to the type of registry used, namely a population-based and a hospital-based registry, respectively. In fact, the study by Dal Maso et al. (10) contained data from a defined geographic area, and not the entire population living near Mt. Vesuvius; therefore, it included few habitants living in the areas where we found a higher risk of DTC. Being a hospital-based registry, our location may have affected the selection of our patients. However, that would not explain our observation of an earlier development of DTC around Mt. Vesuvius.

To determine whether traces of volcanic mineral elements in soils (i.e., selenium, fluorine, vanadium, manganese, and iron) could have entered the aqueduct that serves the areas around Mt. Vesuvius, we analyzed the water from this aqueduct and compared the results to water from the aqueduct that serves other areas of the Campania region. We also analyzed specimens of drinking water from other areas around Mt. Vesuvius, all from the same aqueduct, to evaluate whether patients could have ingested volcanic mineral elements. The concentrations of selenium, vanadium, and manganese were similar in volcanic and in nonvolcanic water, and there was a nonsignificant higher concentration of fluorine and iron in water from volcanic areas versus nonvolcanic areas.

In conclusion, we found a higher risk of papillary thyroid cancer and an earlier onset of this disease in the Vesuvius area than in other areas of Campania, although the risk was not as high as around Mt. Etna. Previous studies suggest that the increased incidence of DTC in volcanic areas could be due to the negative effect of some soil component or radioactivity (9). The vanadium concentration was not increased in our samples, unlike in the Catania study, probably due to the fact that Mt. Etna is a basaltic-active volcano that emits lava, whereas Mt. Vesuvius is dormant (9). Our results show that living in a volcanic area could increase the risk for thyroid cancer, which suggests the need for surveillance of people living in such areas.

A complete thyroid cancer registry in the volcanic areas of Campania and other parts of the world could help to clarify the volcano–thyroid cancer association. An integrated registry from the Vesuvius population-based cancer registry and hospital-based registry could help to shed light on our observation a higher number of patients affected by thyroid cancer in the volcanic areas of Mt. Vesuvius than in the other areas of the Campania region. Lastly, there is a need for studies to identify the potential mechanism by which volcanic environmental factors might favor thyroid tumorigenesis.