# Brown Tumor From Secondary Hyperparathyroidism Mimicking Metastatic Renal Cell Carcinoma in a Patient With End-Stage Renal Disease

## TL;DR

A patient with kidney disease and a history of kidney cancer was found to have rare bone lesions called brown tumors, not cancer spread.

## Contribution

This case highlights the diagnostic challenge of brown tumors mimicking cancer metastases in patients with ESRD and a cancer history.

## Key findings

- Brown tumors were misdiagnosed as metastatic renal cell carcinoma in a patient with ESRD.
- The patient's bone lesions were confirmed to be secondary hyperparathyroidism-related brown tumors.
- The case emphasizes the importance of considering brown tumors in the differential diagnosis of bone lesions in ESRD patients.

## Abstract

Brown tumors (also known as osteitis fibrosa cystica) are rare complications of end-stage renal disease (ESRD) and secondary hyperparathyroidism (HPT), characterized by focal bone lesions that resemble neoplasms. They are often misdiagnosed as metastatic bone disease, especially in patients with a history of malignancy. We present a case of a 60-year-old man with a history of renal cell carcinoma (RCC), and ESRD on hemodialysis (HD), who developed diffuse bone lesions on imaging with osteolytic/osteoblastic appearance concerning metastases, but on further workup was found to have brown tumors. We discuss the treatment and outcome and briefly review the relevant medical literature.