Association between breast cancer and thyroid cancer: a descriptive study

Fang Yu, Jinhua Ma, Kun Huo, Peifeng Li


Background: This study investigated the prevalence and clinicopathological characteristics of patients with breast cancer and thyroid cancer to explore the possible mechanism underlying co-development of these two cancers.
Methods: A retrospective study was performed in 486 female patients with thyroid cancer, among which 8 patients suffered from breast malignancies. The clinicopathological features, hormone receptor status of the invasive breast cancer, and the expression of human mismatch repair genes were analyzed.
Results: The clinicopathological characteristics of thyroid cancer, such as age, clinical stage, lymph node metastasis, and tumor size were not different between the group of patients with both breast and thyroid cancer and the group with thyroid cancer alone. Four cases developed thyroid carcinoma after six months of breast carcinoma diagnosis, three cases developed breast cancer and thyroid cancer simultaneously, and one patient developed breast malignancy after three months of thyroid carcinoma diagnosis. All invasive breast cancers were ER-positive and HER-2 negative. Mutations in human mismatch repair genes were not found for both breast malignancies and thyroid carcinomas.
Conclusions: Co-occurrence of thyroid cancer and breast cancer in the same individual was more frequently observed than expected. Increased surveillance of primary cancer patients may be a significant factor behind the discovery of a second tumor. Estrogen receptor (ER) but not human mismatch repair genes may be involved in the mechanism behind development of co-existing breast cancer and thyroid cancer. Chemotherapy with docetaxel and cyclophosphamide for breast cancer patients might promote the development of thyroid cancer, but some was not related with therapy. Close surveillance of breast and thyroid cancer patients is essential to earlier detecting other secondary tumors.