Prevalence and outcome of metastases to the thyroid gland: a nationwide database study.

OBJECTIVE: Metastases to the thyroid are seen relatively often in autopsy studies. In clinical studies they are described as a rare occurrence. This study aims to provide a more extensive representation of the origin, timing and survival of patients diagnosed with metastases to the thyroid in the Netherlands. METHODS: We performed a retrospective database study using two Dutch nationwide resources. In the Dutch Nationwide Pathology databank (PALGA) database we found 575 patients between 1989 and 2014 with proven metastases to the thyroid. These patient records were then linked with data from the Netherlands Cancer Registry (NCR) to assess whether the presence of these metastases had any impact on patients' survival. 463 patients had complete survival data. RESULTS: The most frequently diagnosed primary tumors were lung (29.4%), kidney (16.5%) and breast carcinoma (10.1%). However, thyroid metastases can originate from any primary. Median time to diagnosis of the thyroid metastasis was 17.2 months after primary diagnosis. In 36 patients the latency period was over 10 years. In 77% of patients, thyroid metastasis was part of pathologically proven widespread disease. Survival after finding the thyroid metastasis was poor, with a median survival of 12.3 months. CONCLUSION: Clinically relevant metastases to the thyroid are relatively rare and occur in a large variety of tumor types. Most of them occur in the context of advanced metastatic disease and therefore prognosis and indication for surgical treatment depend on the extent of the primary tumor, general health of the patient and presence of local symptoms.