High incidence of synchronous or metachronous breast cancer in patients with malignant and benign thyroid tumor or tumor-like disorders.

BACKGROUND Although many reports indicated an association between thyroid diseases and breast cancer, such an association still remains controversial. The present study was aimed to clarify the association of thyroid diseases with the breast cancer incidence. In the patients with benign and malignant thyroid tumor or tumor-like disorders, the incidence of other malignancies was surveyed, and the frequency of thyroid cancer in patients with breast cancer was also surveyed. PATIENTS AND METHODS Between 1982 and 2005, a total of 201 female patients received surgery for tumor or tumor-like disorders, including 65 carcinoma, 68 adenoma, 61 adenomatous goiter and 7 chronic thyroiditis cases. Their outcomes were surveyed in December 2006. Furthermore, during the same periods, 340 female patients underwent breast cancer surgery and their outcomes were also surveyed in December 2006. RESULTS The overall incidence rate of breast cancer was 16.4% (33/201) in the patients, who received thyroid surgeries and was much higher than other malignancies: 2.0% gastric cancer, 1.0% uterine and colorectal cancer. The incidence rate of breast cancer in each disease was 13.8% for thyroid cancer, 16.2% for adenoma and 21.3% for adenomatous goiter, but no incidence for chronic thyroiditis. On the other hand, in the patients with breast cancer during the same period in our department, the frequency of thyroid cancer was only 2.1% (7/340). CONCLUSION It appears that thyroid cancer, adenoma and adenomatous goiter were associated with the risk of breast cancer, but chronic thyroiditis was not related.