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September 12, 1977

Thyroid Hormone and Breast Cancer

JAMA. 1977;238(11):1147. doi:10.1001/jama.1977.03280120039005

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To the Editor. —  Mustacchi and Greenspan observed what appeared to be a high correlation between older ages at breast cancer diagnosis and long duration of thyroid supplement administration.On reanalysis of their data using odds ratio analyses, I came up with a somewhat different interpretation of their findings.If one were to take the observed cases of breast cancer and compare them with the "no cancer" group and analyze them for history and duration of thyroid supplements (all age groups), one finds the following:By this analysis, risk for breast cancer appears to be greater with use and duration of use of thyroid supplements. However, this analysis tells us nothing about age. If, however, one were to split the study and comparison patients into younger and older groups (55 years and younger and over 55 years at diagnosis) one finds the following:One sees by this analysis that the