Early-onset breast cancer in a woman with Graves' disease.

The relationship between thyroid and breast diseases has been documented, but the clinical significance of Graves' disease and breast cancer is unclear. We present a young patient with a history of Graves' disease who developed a multicentric infiltrating ductal carcinoma of the breast several months after discontinuing her treatment with propylthiouracil. Early-onset breast cancer in women without a family history of early breast cancer may be related to hyperthyroidism. The relationship between thyroid hormone and estrogen is discussed.