Metastasis of Solid Tumors to the Thyroid Gland: Report of Two Cases and Review

Abstract

Introduction: Metastases to the thyroid gland from solid malignant tumors are rare, accounting for only 0.13–2% of all thyroid neoplasms. The most common primary tumors include clear cell renal carcinoma, lung, gastrointestinal tumors, melanoma, and, very rarely, breast cancer. Their presentation may be metachronous, synchronous, or even the initial manifestation, and local factors such as preexisting thyroid diseases may favor dissemination. Diagnosis is complex and relies on immunohistochemistry, especially when the primary tumor is not evident. Due to their rarity, these cases merit scientific dissemination in oncology and endocrinology. Case Reports: We present the cases of a 69-year-old male with clear cell renal carcinoma and a 49-year-old female with breast carcinoma, both showing metastases to the thyroid gland. Discussion: Thyroid metastases from solid tumors are uncommon, with renal cell carcinoma being the most frequently involved, followed by breast cancer. Both cases illustrate the phenomenon of metastatic dormancy, with delayed appearance of thyroid lesions. Diagnosis requires a precise immunohistochemical approach to determine the tumor origin. Conclusion: These cases highlight the importance of long-term follow-up in oncology patients, given the risk of delayed thyroid metastases. Differential diagnosis and treatment should be addressed through a multidisciplinary approach, considering both the metastatic origin and the potential coexistence of primary thyroid neoplasms.