DISTANT METASTASIS TO THE THYROID GLAND: CLINICAL REVIEW

Abstract

Background. Metastasis to the thyroid from non-thyroid sites is an uncommon clinical presentation in oncology practice. Renal cell carcinoma is most common primary cancer, followed by breast cancer metastases, small cell lung carcinoma, colorectal cancer, malignant melanoma, malignancies of the gastrointestinal cancer. However, given that thyroid nodules are most common in women, and women with a history of urogenital malignancy are at higher risk of developing thyroid cancer, the possibility of metastatic thyroid cancer must be considered while evaluating a thyroid lump. Aim: to investigate patient management while finding distant metastases to the thyroid and identification of the most common complications. Material and methods. Identified reports of patients with thyroid metastasis were analyzed in the current literature review. Both clinical and autopsy series were included. Results. Metastases to the thyroid gland may be discovered at the time of diagnosis of the primary cancer, after preoperative investigation or due to histological examination of an operative specimen. In autopsy series, the most common primary site of metastatic thyroid tumors is lung cancer. In a clinical setting, renal cell carcinoma is the most common. Otherwise, when patients present with isolated metastases during follow-up of indolent disease, surgery might provide central neck control and even long-term cure. Prognosis may also vary according to the morphological features of primary cancer, time interval between initial diagnosis and metastasis and presence of extrathyroid invasion. Conclusions. Although the thyroid gland is highly vascularized, metastasis of malignant tumors to the thyroid is relatively rare and detection of metastasis shows a low frequency. A past history of malignant neoplasm should raise the index of suspicious of metastatic disease in patients with thyroid nodules with or without cervical lymphadenopathy. In such patients communication among clinicians treating the thyroid and the primary tumor is essential, as there are differences in treatment protocols and prognosis when compared to primary thyroid cancers. The setting is complex, and decisions must be made considering the localization of primary site, features of the primary tumor and comorbidities.  Careful balancing of these factors influences effective patient management and long-term survival.