A rare case of thyroid metastasis occurring 27 years after initial diagnosis of breast cancer: A Case Report

Introduction Breast cancer (BC) most frequently metastasizes to bone, lung, and brain, whereas thyroid involvement is rare. We report a rare case of thyroid metastasis detected 27 years after the initial diagnosis of BC with subsequent pulmonary, cervical lymph node, and skeletal metastases. Case Presentation A 72-year-old woman diagnosed in 1997 with stage IIA, ER-positive, PR-positive, HER2-negative invasive ductal carcinoma underwent modified radical mastectomy followed by adjuvant therapy. After 27 disease-free years, a thyroid nodule was detected. Fine-needle aspiration suggested malignancy, and total thyroidectomy was performed. Immunohistochemistry showed GATA3, ER, and PR positivity with negative HER2, TTF-1, and thyroglobulin, confirming metastatic BC. PET-CT revealed cervical lymph node, pulmonary, and skeletal metastases. The patient received ribociclib, letrozole, and denosumab, with a favorable response at one-year follow-up. Conclusion This case highlights the importance of considering metastatic disease in newly detected thyroid nodules, even decades after the initial diagnosis of breast cancer.