Increased incidence of medullary carcinoma of the thyroid in rural regions in Greece.

A role of environmental factors for the development of Medullary Carcinoma of the Thyroid (MTC) has been shown for animals, but has only been speculated for humans. In the present study we analyzed our registry of 58 sporadic MTCs for the place of origin and place of residence and compared these with 408 other thyroid carcinomas of different histology who are attending the same Endocrine Clinics in the Athens area. Clustering of sporadic MTCs was observed in the Ionian islands, where an increased incidence of familial cases has previously been observed. Patients with sporadic MTCs originated more frequently from rural areas (p = 0.0006), where the main occupation is agriculture. No important differences were observed concerning the place of residence. We speculate that exposure to sunshine, which is greater in rural areas, may be one factor which, through vitamin D, could be involved in the development of C-cell tumors in predisposed individuals.