Mammary gland epithelial changes in thyroidectomized female rats

Purpose: Numerous clinical studies have addressed the relationship of hypothyroidism and breast cancer with conflicting results. In the present experimental study we sought to determine whether absolute hypothyroidism established for a long period of time leads to epithelial alterations of the mammary gland. Methods: Thirty five female Wistar rats were allocated to be subjected to either thyroidectomy (N=20) or not (N=15). The rats were kept alive for a period of 3 months in a weather controlled environment. Serum T3, T4, follicular stimulating hormone (FSH) and estradiol levels were measured at baseline and 10 days after thyroidectomy. Mammary glands were obtained at the end of the experiment and reviewed by an expert pathologist. Results: Both serum FSH and estradiol levels were lower 10 days after thyroidectomy; however, only FSH values were significantly lower in the thyroidectomized animals. Pathological analysis revealed significantly increased atrophy and periductal fibrosis of the mammary gland among thyroidectomized animals. Conclusion: This is the first in vivo experimental study that reveals an association between the thyroid and mammary glands. Future studies should address the proteomic relationship that connects them.