Not So Clear Cut: A Case Report of Hypothyroidism Associated with Clear Cell Renal Cell Carcinoma Metastatic to the Thyroid

The incidence of metastases to the thyroid gland is approximately 2 % based on prior autopsy series. Of these, renal cell carcinoma is the most likely cancer to metastasize to the thyroid gland. We describe a case of a large thyroid mass in a patient with renal cell carcinoma and subclinical hypothyroidism who developed profound hypothyroidism with immune checkpoint inhibitor use.

Case Description:

A 78-year-old man with a medical history of subclinical hypothyroidism and metastatic clear cell renal cell carcinoma to subcutaneous tissues of the left flank presented with severe depression, fatigue, cold intolerance, and dry skin. He was found to have profound hypothyroidism in the setting of immune checkpoint inhibitor use with a TSH of 90.48 mIU/L and a free t4 of 0.8 ng/dL. He had been diagnosed with clear cell renal cell carcinoma two years prior and undergone a nephrectomy with negative surgical margins. Surveillance imaging one year later showed a left flank mass with a subsequent biopsy showing metastatic renal cell cancer. Six months later, chest cross-sectional imaging found a large heterogeneous enhancing left-sided thyroid mass measuring 4.9 x 4.3 x 7.9 cm with an area of central necrosis. He underwent a biopsy of this mass which demonstrated metastatic renal clear cell carcinoma. He started combination immunotherapy with nivolumab and ipilimumab. The patient had overt hypothyroidism prior to starting immunotherapy, with TSH of 9.86 mIU/L, free t4 0.7 ng/dL, concerning for hypothyroidism related to compression from mass. After five months of treatment, the thyroid mass had significantly decreased in size. Thyroid function improved with levothyroxine supplementation. The patient, unfortunately, succumbed to his malignancy. He did not have an evaluation for autoantibodies prior to his death.

Discussion:

Patients with thyroid cancer, thyroiditis, and goiter are thought to be susceptible to metastases as in the case described above. There is also the potential that metastases to the thyroid may precipitate thyroiditis. This case is unique as we suspect the large size of the thyroid mass contributed to overt hypothyroidism. The patient went on to develop profound hypothyroidism, likely from thyroiditis in the setting of immune checkpoint inhibitor use.