Metastasis to the thyroid diagnosed by fine‐needle aspiration biopsy

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Abstract
Background Metastasis to the thyroid is uncommon, but the number of cases seems to have increased in recent years. This increase may be related to more frequent use of fine‐needle aspiration biopsy (FNAB) in any suspected case. Design A retrospective review of patients with thyroid metastasis diagnosed by FNAB at the Asan Medical Centre. Patients Twenty‐two patients who were seen at the Asan Medical Centre between 1997 and 2003. Median age was 55 years with range between 34 and 74 years. Results Fourteen patients presented with a palpable thyroid nodule. Eight patients had an impalpable thyroid nodule that was found incidentally during the various imaging studies. The breast (five patients) was the most common primary site followed by the kidney (three), colon (three) and lung (three). FNAB confirmed metastatic disease in 19 patients and raised suspicion in three patients. The suspicion of metastasis to the thyroid was confirmed by Tru‐cut needle core biopsy in one patient and surgery in two patients. Thyroid metastases were found during the initial work‐up for primary tumour in eight patients. In the remaining 14 patients, the interval from diagnosis of primary tumour to the detection of thyroid metastasis varied from 8 months to 15 years, with a median of 54 months. Fifteen patients had metastatic disease elsewhere at the time of presentation. Ten patients received chemotherapy. Radiotherapy was used in two patients. Seven patients are still alive, with one patient disease free for 16 months following resection of the thyroid metastasis. Conclusions Thyroid metastases are uncommon but can be detected more frequently with routine use of FNAB. Breast cancer is the most common tumour that metastasizes to the thyroid. They usually occur when there are metastases elsewhere, sometimes many years after the diagnosis of the original primary tumour and show poor prognosis in general.