Endocrine Abstracts

Introduction: Subacute thyroiditis (SAT) association with papillary thyroid carcinoma (PTC) has been rarely reported in the literature. Metastatic neoplasms to the thyroid are rare in clinical practice. Renal cell carcinomas (RCC) are the most frequent site of origin of thyroid metastases (12 to 34%). Tumor-to-tumor metastases, in which a thyroid neoplasm is the recipient of a metastasis, are exceedingly rare. Tuberous sclerosis (TS) is associated with several renal manifestations (80–85% of the patients) including angiomyolipomas (AMLs) (80%), renal cysts (30%) and RCC (2–4%)

Case report: A 19-year-old male, with personal history of TS, presented in the emergency department complaining of edema, jitteriness and pain in cervical region. SAT diagnosis was established based on complaints, physical examination and laboratory results. After the resolution of SAT, thyroid ultrasonography (US) revealed 2 suspicious nodules. The major nodule was submitted to fine needle aspiration cytology and the report was suspected of malignancy. Total thyroidectomy was performed. Postsurgical pathology evaluation showed a bilateral PTC/follicular variant (pT3N0). Within the PTC were a few nests of a morphologically distinct neoplasm. Immunoperoxidase stains of these cells were positive for CK8/18 and CK7 and were negative for thyroglobulin, calcitonin, vimentin, CK20, CD10 and racemase thus suggesting metastases of RCC. The body CT showed bilateral renal lesions likely to be angiolipomas without distinctive criteria. Suspicious lesions in the liver, lungs and bones were also reported without uptake in a 18F-FDG PET-CT.

Conclusion: This case illustrates an extremely rare occurrence of tumor-to-tumor metastasis where the recipient was a PTC and the donor likely to be an occult RCC.