Thyroid metastasis from breast cancer presenting with enlarged lateral cervical lymph nodes: A case report

BACKGROUND Secondary malignancy of the thyroid occurs infrequently and mainly originates from malignant tumors of the kidney, gastrointestinal tract, lungs, breast, and skin. The correct diagnosis is important but difficult. Importantly, there are major differences in the treatment of primary and metastatic thyroid cancer, which has a significant impact on prognosis and survival. Therefore, how to diagnose thyroid metastasis (TM) correctly before surgery is a major concern for surgeons. CASE SUMMARY We report a 38-year-old woman who presented with palpable cervical lymph nodes after breast cancer (BC) surgery 2 years ago. Ultrasonography and computed tomography revealed thyroid nodules with irregular margins and enlarged cervical lymph nodes. Biopsy was performed for the right largest cervical lymph node, and immunohistochemical analysis revealed negativity for thyroglobulin, estrogen receptor, and progestin receptor and positive for human epidermal growth factor receptor 2. The diagnosis was TM from BC with cervical lymph node metastasis. Total thyroidectomy with bilateral central and lateral neck lymph node dissection was performed. After a 5-mo follow-up, no recurrence or novel distant metastasis was identified. CONCLUSION TM from BC is a rare secondary malignancy. Broad differential diagnosis by biopsy and immunohistochemical analysis needs to be considered.