Gender is an Age-Specific Effect Modifier for Papillary Cancers of the Thyroid Gland
- Briseis A. Kilfoy1,3,
- Susan S. Devesa2,
- Mary H. Ward1,
- Yawei Zhang3,
- Philip S. Rosenberg2,
- Theodore R. Holford3 and
- William F. Anderson2
- 1Occupational and Environmental Epidemiology Branch and 2Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland; and 3Yale School of Public Health, Yale University, New Haven, Connecticut
- Requests for reprints:
Briseis A. Kilfoy, Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, EPS, Room 8091, 6120 Executive Boulevard, Bethesda, MD 20852-7244. Phone: 301-451-5031; Fax: 301-402-1819. E-mail: kilfoyb{at}mail.nih.gov
Abstract
Background: Thyroid cancer incidence rates have increased worldwide for decades, although more for papillary carcinomas than other types and more for females than males. There are few known thyroid cancer risk factors except female gender, and the reasons for the increasing incidence and gender differences are unknown.
Methods: We used the National Cancer Institute's Surveillance, Epidemiology, and End Results 9 Registries Database for cases diagnosed during 1976-2005 to develop etiological clues regarding gender-related differences in papillary thyroid cancer incidence. Standard descriptive epidemiology was supplemented with age-period-cohort (APC) models, simultaneously adjusted for age, calendar-period and birth-cohort effects.
Results: The papillary thyroid cancer incidence rate among females was 2.6 times that among males (9.2 versus 3.6 per 100,000 person-years, respectively), with a widening gender gap over time. Age-specific rates were higher among women than men across all age groups, and the female-to-male rate ratio declined quite consistently from more than five at ages 20-24 to 3.4 at ages 35-44 and approached one at ages 80+. APC models for papillary thyroid cancers confirmed statistically different age-specific effects among women and men (P < 0.001 for the null hypothesis of no difference by gender), adjusted for calendar-period and birth-cohort effects.
Conclusion: Gender was an age-specific effect modifier for papillary thyroid cancer incidence. Future analytic studies attempting to identify the risk factors responsible for rising papillary thyroid cancer incidence should be designed with adequate power to assess this age-specific interaction among females and males. (Cancer Epidemiol Biomarkers Prev 2009;18(4):1092–100)
Footnotes
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↵4 C. Zhu, T. Zheng, B.A. Kilfoy, et al. Birth Cohort Analyses of the Incidence of Papillary Thyroid Cancer by Gender and Histological Subtypes in the United States, 1973–2004. Submitted.
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↵5 L. Enewold, K. Zhu, E. Ron, et al. Rising thyroid cancer incidence in the United States by demographic and tumor characteristics, 1980–2005. Cancer Epidemiol Biomarkers Prev. 2009 Mar;18(3):784-91. Epub 2009 Feb 24.
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Grant support: Intramural Research Program of the National Institutes of Health, National Cancer Institute. The authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
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- Accepted January 27, 2009.
- Received October 15, 2008.
- Revision received January 14, 2009.
