A case of breast metastasis from follicular thyroid carcinoma: a rare and delayed complication of thyroid cancer

Abstract Background: Follicular thyroid carcinoma (FTC) is a type of differentiated thyroid cancer that can metastasize to distant organs via hematogenous spread. Breast metastasis from FTC is an extremely rare but possible complication that can mimic primary breast cancer. Case Presentation: We present a case of a 64-year-old woman who had a history of subtotal thyroidectomy for FTC 17 years ago and developed a palpable mass in her left breast. Ultrasound, mammography and fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) showed an irregular nodule with calcifications and increased FDG uptake in the left breast, as well as hypermetabolic nodules in the right lower lung and thyroid gland. The patient underwent total thyroidectomy and left segmental mastectomy, and the pathology confirmed the diagnosis of FTC recurrence and breast metastasis. The patient received three cycles of I-131 radioablation therapy and thyroid stimulating hormone (TSH) suppressive therapy, and achieved complete remission of the recurrent FTC lesion and breast metastasis. Conclusions: This case highlights the importance of considering the possibility of breast metastasis from FTC in patients with a history of thyroid cancer and a suspicious breast mass. FDG PET/CT can provide valuable information for the diagnosis and staging of FTC breast metastasis. Total thyroidectomy, segmental mastectomy, I-131 radioablation therapy and TSH suppressive therapy can be an effective treatment option for this rare condition.