Incidence rates have increased considerably worldwide for both differentiated thyroid cancer and cutaneous melanoma, and two-way associations between these neoplasms have been described. Whether melanoma risk factors are associated with thyroid cancer risk remains unknown.
Using Cox regression modeling, we prospectively analyzed the relationship between self-reported pigmentary traits, baseline residential ultraviolet (UV) exposure, and thyroid cancer risk in 86,960 women from the E3N cohort, followed-up over 1990–2008 through biennial questionnaires. We assessed associations of pigmentary traits and UV exposure with personal history of benign thyroid diseases using logistic regression modeling. All statistical tests were two sided.
In models adjusted for age and thyroid cancer risk factors, number of nevi was positively associated with thyroid cancer risk (“very many” vs. “none”: hazards ratio [HR] = 1.7, 95% confidence interval [CI] = 1.0, 2.8; Ptrend = 0.01), independently of residential UV exposure or iodine intake. Risk was inversely associated with latitude and positively associated with mean daily UV level at baseline (HRs for the fourth vs. first quartile of latitude and spring/summer UVB level = 0.7, 95% CI = 0.5, 0.9; Ptrend = 0.03, and HR = 1.9, 95% CI = 1.4, 2.7; Ptrend = 0.02, respectively); associations were restricted to women with dietary iodine below the median intake. Number of nevi and UV level were also associated with personal histories of dysthyroidism and of goiter/nodules, although more weakly so.
Our results suggest that number of nevi and residential UV exposure are associated with the risks of thyroid cancer and benign conditions. They point to novel pathways in thyroid cancer or melanoma etiologies and warrant replication.
From the aUniversité Paris-Saclay, University of Paris-Sud, UVSQ, Inserm, CESP, Generations and Health Team, Villejuif, France; bGustave Roussy, Villejuif, France; cHôpital Bretonneau, CHRU de Tours, Gynécologie-Obstétrique, Tours, France; and dMINES ParisTech, PSL-Research University, O.I.E. – Centre Observation, Impacts, Energy, Sophia Antipolis, France.
Submitted 18 November 2015; accepted 3 April 2017.
Supported by the Mutuelle Générale de l’Education Nationale (MGEN); the European Community; the French League against Cancer (LNCC); Gustave Roussy; and the French National Institutes for Health and Medical Research (Inserm). M.K. was supported by a Marie Curie Fellowship within the 7th European Community Framework Programme (#PIOF-GA-2011–302078). The present study received grant support from the French National Cancer Institute (InCA) (#2009–139).
The authors report no conflicts of interest.
The authors Mesrine and Kvaskoff contributed equally to this study.
Data are available for replication purposes from the corresponding author.
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Correspondence: Marina Kvaskoff, Inserm, CESP “Generations and Health” Team, Gustave Roussy, 114, rue Edouard Vaillant, F-94805 Villejuif Cedex, France. E-mail: firstname.lastname@example.org.