Background: The incidence of metastatic breast cancer tumors in the thyroid gland is very rare, however, invasive micropapillary carcinoma of breast metastasizes to thyroid gland is rarer. As far as we know, there has never been reported that both invasive ductal carcinoma– no special type (IDC-NST) and invasive micropapillary carcinoma (IMPC) exist in breast whereas only the latter metastasizes into the thyroid gland.
Case presentation: we report a case of a 59-year-old Chinese woman first diagnosed as IDC-NST of breast with involvement of axillary lymph node, grade 2 in 2015. However, five years later, blood tests revealed increased tumor markers. Multiple solid nodules were found in both side of thyroid gland by imaging. Total thyroidectomy and bilateral cervical lymph nodes dissection were presentation: the findings showed both IDC-NST and IMPC in lymph nodes but only the later in thyroid gland. Immunohistochemically, these tumor cells were positive for ER, PR, GATA3 and Mammaglobin, but negative for TG and TTF-1. Ultimately, the patient was diagnosed as mixed breast cancer with metastatic IMPC in thyroid and radiation therapy was still continued.
Conclusion: Apart from the possibility of metastatic no special type of breast cancer to thyroid tumor, IMPC of breast metastasis must be taken into consideration, especially when the patient has a history of breast cancer and thyroid nodes. Accurate diagnose of metastatic breast carcinoma is vital for precise treatment and can improve the prognosis for patients.