# Hidden in Plain Sight: Metastatic Renal Cell Carcinoma Masquerading as Multinodular Thyroid Disease

## TL;DR

A rare case of kidney cancer spreading to the thyroid was mistaken for thyroid disease, highlighting the need for careful monitoring in cancer survivors.

## Contribution

This case highlights the unusual presentation of metastatic renal cell carcinoma mimicking thyroid disease.

## Key findings

- Renal cell carcinoma can metastasize to the thyroid after a prolonged dormancy.
- Metastatic RCC may present as multinodular thyroid disease, leading to diagnostic challenges.
- PSMA PET imaging helped detect thyroid nodules that were later confirmed as RCC metastases.

## Abstract

Metastases to the thyroid gland are uncommon, with renal cell carcinoma (RCC) representing a rare but clinically significant occurrence. RCC may metastasize after a prolonged dormancy and remain clinically silent for years before detection. We present a case of a 61-year-old man who initially presented with hematuria. Imaging at the time revealed RCC confined to the kidney. Several years later, during surveillance imaging for newly diagnosed prostate cancer via prostate-specific membrane antigen (PSMA) positron emission tomography (PET), bilateral thyroid nodules were incidentally detected. Histopathological examination of the resected multinodular thyroid revealed an unexpected finding of metastatic RCC, initially masquerading as a primary thyroid neoplasm. Awareness of RCC’s propensity to masquerade as a primary thyroid tumor is paramount for the surveillance and management of patients with a history of RCC.