Endocrine Abstracts

Metastatic disease to the thyroid is rare, accounting for 2–3% of thyroid malignancy. The most common malignancy to metastasise to thyroid is renal cell carcinoma (48.1%), followed by colorectal (10.4%) and lung (8.3%). Clinically, clear cell renal cell carcinoma (CCRCC) can present with thyroid metastases years or decades later. Several studies have shown that thyroid gland abnormalities, including nodular goitre or thyroiditis, are more likely to harbour metastases.

A 68 year old lady with no past medical history was found to have an incidental grade 2, pT1b clear cell carcinoma of the kidney during investigation of back pain with MRI spine. Staging investigations demonstrated no macroscopically visible distant metastases. It did however demonstrate the presence of a multi-nodular goitre. She underwent total nephrectomy and remained well.

Five years later she was referred to ENT with haemoptysis. No cause was found, but once again CT demonstrated multi-nodular goitre. Simultaneously she was referred to endocrinology with subclinical thyrotoxicosis (TSH <0.01, fT4 21.1). Antibody testing was negative and uptake scan normal. Ultrasound revealed a left goitre composing of multiple colloid nodules and several hypoechoic nodules. FNA on two separate occasions (THY3a, THY1) failed to yield definitive diagnostic material, and she underwent diagnostic left hemithyroidectomy.

The pathology showed nodular thyroid hyperplasia with numerous metastatic deposits of CCRCC. The pathology was positive for CD10, and negative for thyroglobulin.

The patient has now undergone completion thyroidectomy, and at this moment has no evidence of ongoing disease or requirement for systemic therapy.

This case highlights that metastatic renal cell carcinoma to the thyroid should be considered in any patient with a history of malignancy and thyroid abnormalities, regardless of the duration since the primary diagnosis. Prognosis is favorable following thyroidectomy in the absence of other metastases.