Relationship of Gender and Smoking History in the Development of Hypothyroidism From Exposure to External Beam Radiation for Head and Neck Cancers

Background: Patients with head and neck cancers (HNCs) are often treated with external beam radiation therapy (XRT). Unfortunately this therapy is not without its unintended consequences. One of these side effects includes the development of radiation-induced hypothyroidism. Our study is designed to pay special attention to variables like gender and smoking history and analyze their relationship with the development of hypothyroidism. Methods: Patients’ charts were reviewed over a period of 13 years from January 1, 2000 to November 30, 2013 to gather information on patients who had previously received XRTs for HNCs. We used the Tumor Registry Database at the University of Florida, College of Medicine in Jacksonville for this retrospective review. Patient characteristics were examined including age, gender, race/ethnicity and smoking history. Special attention was paid to the development of hypothyroidism (thyroid stimulating hormones > 5.0 with appropriate decrease in free serum T4) levels after exposure to XRT for HNCs. Results were then analyzed using the univariate statistical analysis which was done using the SAS software using a 0.05 alpha level of significance expressed in terms of odds ratio (OR) with 95% confidence intervals (CIs). Results: We found a total of 1,116 patients in our database who have received XRTs for HNCs. Out of these 72 (6.45%) patients developed hypothyroidism. Out of 263 African American patients 20 (7.6%) had hypothyroidism, whereas 49 (6%) out of 819 white people had this outcome. As for gender 32 out of 341 females (9.4%) and 40 out of 775 males had hypothyroidism. Thirty-five out of 544 (6.4%) with no family history and 19 (2.4%) out of 205 (9.3%) with positive family history for cancer had the outcome too. Finally 43 (6.5%) out of 664 smokers and 17 (8.3%) out of 206 non-smokers were found to develop hypothyroid as well. Both groups were found to have homogenous average age at diagnosis. When the univariate analysis was conducted, the strongest predicting variable was gender as hypothyroid patients were 1.90 (95% CI 1.17 - 3.09) times more likely to be females, and these results were statistically significant with P value of 0.008. More patients tended to be African Americans with OR 1.21 (CI 0.822 - 1.78), had positive family history of cancer (negative family history had OR 0.67 (CI 0.38 - 1.21), and less likely to be smokers (OR 0.77 (0.43 - 1.38). However, race, family history of cancer and smoking history did not achieve any statistical significance as evident by the P values. World J Oncol. 2014;5(3):113-117 doi: http://dx.doi.org/10.14740/wjon835w