Chieh-Chen Wu1,2, Ya-Yu Yu3, Hsuan-Chia Yang4,2, Phung Anh Nguyen2,5, Tahmina Nasrin Poly1, Md Mohaimenul Islam1,2, Usman Iqbal2,6, Hafash Arshed Ali Khan2, Yao-Chin Wang1,7, Yung-Tzu Cheng1,8, Yu-Chuan Li9,10, Wen-Shan Jian11,12. 1. Graduate Institute of Biomedical Informatics, College of Medicine Science and Technology, Taipei Medical University, Taipei, Taiwan. 2. International Center for Health Information Technology (ICHIT), Taipei Medical University, Taipei, Taiwan. 3. Tri-Service General Hospital, Songshan Branch, Taipei, Taiwan. 4. College of Medicine Science and Technology, Taipei Medical University, Taipei, Taiwan. 5. Department of Population and Quantitative Health Sciences, Case Western Reserve University, Cleveland, USA. 6. Master's Program in Global Health and Development Department, College of Public Health, Taipei Medical University, Taipei, Taiwan. 7. Department of Emergency, Min-Sheng General Hospital, Taoyuan, Taiwan. 8. Department of Laboratory Medicine, Cathay General Hospital, Taipei, Taiwan. 9. Graduate Institute of Biomedical Informatics, College of Medicine Science and Technology, Taipei Medical University, Taipei, Taiwan. jack@tmu.edu.tw. 10. International Center for Health Information Technology (ICHIT), Taipei Medical University, Taipei, Taiwan. jack@tmu.edu.tw. 11. International Center for Health Information Technology (ICHIT), Taipei Medical University, Taipei, Taiwan. jjtmutw@gmail.com. 12. School of Health Care Administration, Taipei Medical University (TMU), No. 172-1, Section 2, Keelung Road, Da'an District, Taipei, 10675, Taiwan. jjtmutw@gmail.com.
Abstract
PURPOSE: To investigate whether the use of levothyroxine was associated with breast cancer risk. METHODS: We conducted a population-based case-control study in Taiwan. Cases consisted of all patients who were aged 20 years and older, and had a first-time diagnosis of breast cancer for the period between 2001 and 2011. The controls were matched to the cases by age, sex, year, and month of diagnosis. Adjusted odd ratios (ORs) and 95% confidence intervals (CIs) were estimated by a conditional logistic regression. RESULTS: We examined 65,491 breast cancer cases and 261,964 controls. We found that use of levothyroxine was associated with a significant increase in breast cancer risk (OR 1.24, 95% CI 1.15-1.33; P < 0.001). Compared with no use levothyroxine, the adjusted odd ratio was 1.22 (95% CI 1.11-1.35; P = 0.01) for the group having been prescribed levothyroxine 2 months to 1 year, and 1.26 (95% CI 1.12-1.41; P < 0.01) for the group with more than 1 year. When stratified by age, the adjusted odd ratio was 1.45 (95% CI 1.23-1.71; P < 0.01) for the patients aged 65 years or more and 1.19 (95% CI 1.09-1.29, P < 0.01) for the patients aged less than 65 years. CONCLUSION: The results of the present study are the first to suggest that levothyroxine use increased the risk of breast cancer. However, a larger long-term prospective randomized-controlled trial specifically designed to assess the effect of levothyroxine use on the risk of developing breast cancer is needed.
PURPOSE: To investigate whether the use of levothyroxine was associated with breast cancer risk. METHODS: We conducted a population-based case-control study in Taiwan. Cases consisted of all patients who were aged 20 years and older, and had a first-time diagnosis of breast cancer for the period between 2001 and 2011. The controls were matched to the cases by age, sex, year, and month of diagnosis. Adjusted odd ratios (ORs) and 95% confidence intervals (CIs) were estimated by a conditional logistic regression. RESULTS: We examined 65,491 breast cancer cases and 261,964 controls. We found that use of levothyroxine was associated with a significant increase in breast cancer risk (OR 1.24, 95% CI 1.15-1.33; P < 0.001). Compared with no use levothyroxine, the adjusted odd ratio was 1.22 (95% CI 1.11-1.35; P = 0.01) for the group having been prescribed levothyroxine 2 months to 1 year, and 1.26 (95% CI 1.12-1.41; P < 0.01) for the group with more than 1 year. When stratified by age, the adjusted odd ratio was 1.45 (95% CI 1.23-1.71; P < 0.01) for the patients aged 65 years or more and 1.19 (95% CI 1.09-1.29, P < 0.01) for the patients aged less than 65 years. CONCLUSION: The results of the present study are the first to suggest that levothyroxine use increased the risk of breast cancer. However, a larger long-term prospective randomized-controlled trial specifically designed to assess the effect of levothyroxine use on the risk of developing breast cancer is needed.
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Keywords:
Breast cancer; Case–control study; Levothyroxine; Odd ratio; Thyroid disease