YO39 - Primary Follicular Thyroid Carcinoma Metastatic to the Kidney Mimicking Renal Cell Carcinoma: A Case Report

Case summary

Background: Follicular thyroid carcinoma commonly presents with hematogenous metastasis to the lung and bone and rarely to the kidney. We report a case of a 61-year old woman with a metastatic follicular thyroid carcinoma to the kidney. This case report shows how a systematic approach on a patient with a renal mass can lead to a diagnosis of an unexpected primary cancer.

Case Report: A 61-year old female presented with progressively enlarging back mass. Whole abdominal ultrasound revealed right renal mass; chest CT scan showed multiple heterogeneously varisized pulmonary nodules. Ct-guided fine needle aspiration biopsy of the lung nodule was compatible with a non-small cell carcinoma. Immuno-histochemistry was positive for CK7, TTF1 and thyroglobulin and CK 20 negative favoring metastatic thyroid carcinoma. Ultrasound-guided core needle biopsy of the renal mass was compatible with thyroid carcinoma, metastatic (thyroglobulin positive). The final histopathology report after thyroidectomy was non-invasive follicular thyroid neoplasm with papillary-like nuclear features. The patient received radioactive iodine and is now with better quality of life.

Discussion: Metastatic follicular thyroid carcinoma is a rare phenomenon with only 25 cases reported in the English literature to date. Johnson et al in 1982 reported a case of follicular thyroid carcinoma with metastasis to the kidney 37 years after resection of the primary tumor. In a study by Parameswaran in 2016 on patterns of metastasis in follicular thyroid carcinoma, they found out that 40% of cases metastasized at a median of 4.5 years after initial thyroidectomy, lungs being the most common site followed by bone (25%), regional lymph nodes (13%) and brain (12%). None of the said cohort had metastasis to the kidney. The best management of FTC presenting as metastatic disease should be managed aggressively with total thyroidectomy followed by RAI which was done in our patient.

Conclusion: Given the rarity of thyroid metastasis to the kidney, a diagnostic dilemma for this case was a challenge. This case provides new data to clinicians that thyroid carcinoma can metastasize to the kidney and may mimic renal cell carcinoma although rarely reported.

Clinical trial identification

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