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To the Editor.—
The article by Kapdi and Wolfe provides some very interesting data, but in order to assess its clinical and epidemiologic significance, we would like to make the following observations.First, it is very important to note that women receiving thyroid medication are older than the control group of women not receiving thyroid medication (median age of 46 to 55 years vs 35 to 45 years). Also, women taking thyroid medication for more than 15 years are older than women taking the medication for less than 15 years (in the group receiving thyroid medication for 1 to 5 years, 47% are >45 years old; receiving thyroid medication for 6 to 15 years, 60% are >45 years old; and receiving thyroid medication for >15 years, 75% are >45 years old).Since the risk of developing breast cancer increases with age and length of exposure to thyroid medication is directly
Farber MD, Visscher B. Thyroid Supplements and Breast Cancer. JAMA. 1976;236(24):2744-2745. doi:10.1001/jama.1976.03270250013008