Association Between Papillary Thyroid Cancer and Allergy: A Case-Control Study

Background: Thyroid cancer incidence has dramatically increased in many countries. Several studies have investigated the association between cancer and allergy, and most of them have had equivocal results. Objectives: The aim of this study was to evaluate the association between allergy and papillary thyroid cancer (PTC). Methods: This case-control study was performed among 3 university hospitals of Tehran. Cases (n = 59) were selected among patients with PTC based on final pathology after thyroidectomy. Controls (n = 53) consisted of patients attending the outpatient’s clinics of the same hospitals with no symptoms of any cancer. Data about allergic diseases and symptoms were collected by a modified International Study of Asthma and Allergy in Childhood (ISAAC) questionnaire. Results: Logistic regression analysis manifested the reverse associationbetweenallergic rhinitis(OR=0.07, 95% CI: 0.007 - 0.74) with PTC considering confounding variables (age, body mass index (BMI), and family history of thyroid cancer in first degree relatives). In addition, we found the reverse association between any allergy and PTC in this population (OR = 0.25, 95% CI: 0.1 - 0.64). Meanwhile, the results in both models revealed a reverse association between BMI (OR < 1, P < 0.05) and PTC. Finally, family history of thyroid cancer had a significant relationship with developing thyroid cancer in our population (OR > 6, P < 0.05). Conclusions: Our data suggest a reverse association between allergy diseases, specifically allergic rhinitis and suffering from thyroid cancer. However, further studies are required to clarify association observed between PTC and allergy considering environmental and host factors.