Metastatic renal cell carcinoma to the thyroid gland with tracheal invasion: A case report

Renal cell carcinoma (RCC) is the most common neoplasm of the kidney. It often manifests with nonspecific symptoms, and most cases are incidentally identified during abdominal imaging for unrelated etiologies. Radiologically, it typically presents as a hypervascular, solid, or cystic mass with heterogeneous features. The current standards of treatment vary depending on whether the malignancy is localized or not, but options include radical or partial nephrectomy, radiotherapy, immuno-oncological agents, and tyrosine kinase inhibitors. The likelihood of metastasis in RCC is positively correlated with lesion size, and metastasis most frequently occurs to the lungs, lymph nodes, bones, and liver. Metastasis at other sites, including the thyroid gland, is rare and has not been extensively documented. We present the unusual case of a 76-year-old female with metastatic RCC (mRCC) to the thyroid gland with direct tracheal invasion. Though the patient's initial clinical presentation favored anaplastic thyroid carcinoma, further analysis prompted a final diagnosis of metastatic RCC. This case highlights the crucial roles of imaging, pathological study, and innovative therapies to facilitate accurate diagnosis and optimal treatment of this rare clinical presentation.