Tumor-to-Tumor Metastasis: Lung Carcinoma Metastasizing to Thyroid Neoplasms

Tumor-to-tumor metastasis is extremely rare in the thyroid glands, and only seven cases of lung carcinoma metastasizing to thyroid tumors have been reported in the literature. We report another two cases of lung carcinoma metastasizing to thyroid neoplasms and review of the literature. The first case was a 64-year-old man presenting with neck mass, hoarseness, and easy choking for 2 months. Image studies showed several nodular lesions within bilateral thyroid glands. A histological examination after radical thyroidectomy revealed lung small cell carcinoma metastasizing to a thyroid follicular adenoma. The second case was a 71-year-old woman with a history of lung adenosquamous carcinoma. The PET/CT scan showed left lower lung cancer and a hypermetabolic area in the right thyroid lobe, highly suspicious for malignancy. Radical thyroidectomy and left lung lobectomy were performed, and the thyroid gland revealed lung adenosquamous carcinoma metastasizing to a papillary thyroid carcinoma.