Metastasis to the thyroid gland: Characterization and survival of an institutional series spanning 28 years.

INTRODUCTION: Secondary neoplasms in the thyroid are rare. The study aim was to provide an overview of non-thyroid tumours that metastasize to the thyroid through our institutional experience.

MATERIALS AND METHODS: This study entailed a review of the pathology database searching for patients with metastasis to the thyroid at the Karolinska University Hospital between 1992 and 2019 and review of their medical files.

RESULTS: Out of 1939 surgical procedures with a histopathological diagnosis of a thyroid malignancy, 31 cases (1.6%, 65% females) with a diagnosis of metastatic epithelial neoplasms to the thyroid gland were identified. The median age at discovery of the thyroid metastasis was 68 years (range 48-85). The most common primary tumours were clear cell renal cell carcinoma (ccRCC) (36%), followed by non-small cell lung cancer (19%), oesophageal cancer (16%), head and neck malignancies (16%), malignant melanoma (10%) and unknown primary tumour (3%). The median time from the diagnosis of the primary tumour to diagnosis of the thyroid metastasis was 20 months (0-232) and was longest for patients with ccRCC (median 107 months). At 12 months after the non-thyroid metastasis diagnosis 48% had died. The longest survival was observed in ccRCC and the shortest in lung cancer. Surgical management of the metastasis was associated with improved survival (25 vs 3.8 months, p = 0.001).

CONCLUSIONS: Non-thyroid metastases to the thyroid were rare but should be suspected in patients with previous history of non-thyroid malignancy and a thyroid nodule. Prognosis was poor, but surgical management was beneficial in selected patients.