Iodine intake as a risk factor for BRAF mutations in papillary thyroid cancer patients from an iodine-replete area

Abstract

Both deficient and excessive iodine intake leads to thyroid disease, which shows U-shaped curves. Our previous study showed that a relatively low [urinary iodine concentration (UIC) < 300 mu g/L] and extremely excessive (UIC2500 mu g/L) iodine intake were associated with thyroid cancer in Korea, an iodine-replete area. Papillary thyroid cancer (PTC) accounts for more than 97 % of thyroid cancer and 80% or more PTC cases harbor the BRAF mutation in Korea. We aimed to investigate the relationship between iodine intake and the prevalence of the BRAF mutation in PTC in Korea. UIC was measured by inductively coupled plasma mass spectrometry. The BRAF mutation was detected using both allele-specific polymerase chain reaction and mutant enrichment with 3'-modified oligonucleotide sequencing. Risk factors for the occurrence of BRAF mutations in PTC were evaluated using multivariate logistic regression models. The median UIC in all patients with PTC was 287 mu g/L (range from 7 to 7, 426 mu g/L). Nearly half of the patients (102/215, 47%) belonged to the excessive iodine intake category (UIC300 mu g/L) according to the WHO iodine recommendations. The frequency of BRAF mutations was lowest in the 300-499 mu g/L UIC group; it was significantly different compared to the relatively low (UIC < 300 mu g/L) and more than excessive (UIC500 mu g/L) iodine intake groups. UIC was an independent predictor for BRAF mutations in PTC. The multivariate-adjusted odds ratios (95% confidence intervals) in the relatively low and more than excessive iodine intake groups for the BRAF mutation were 4.761 (1.764-12.850) and 6.240 (2.080-18.726), respectively, compared to the 300-499 mu g/L UIC group. Relatively low iodine intake and more than excessive iodine intake seem to be significant risk factors for the occurrence of BRAF mutations in the thyroid and, therefore, may be risk factors for the development of PTC in an iodine-replete area.