A case of renal carcinoma metastasis simulating a thyroid goiter

Background: Although the thyroid is a highly vascularized gland, it is not a common target of metastasis from extrathyroidal cancer. Clear-cell renal carcinoma (cRCC) frequently metastasizes to the thyroid, representing 2-3% of all adult tumors, and more than 40% of patients present with metastases at diagnosis. The presence of cRCC thyroidal metastases makes the differential diagnosis from thyroid clearcell carcinoma extremely difficult. Patients and Methods: A 70-year-old woman presented with a mild compressive symptomatology due to a recent multinodular thyroid goiter with a ‘simple’ multinodular ultrasound pattern, in the absence of signs of malignancy and with normal findings for hormonal and immunological assessment. Clinical history presented chronic renal failure under hemodialytic treatment subsequent to a right nephrectomy carried out 2 years before for an unspecified cause. A volumetric increase of the whole gland was evident, with absence of laterocervical adenopathy. A total thyroidectomy was performed. Results: Histological examination showed an enlargement of the thyroid with a distorted shape; the cross-section showed multiple nodules, some with firm appearance and others with colloidal appearance. The sections showed nodules with firm appearance surrounded by a complete fibrous capsule and characterized by proliferation of large cells, with abundant optically clear cytoplasm and well-defined margins, arranged in an alveolar-tubular pattern (nests and cords). The nuclei exhibited mild to moderate atypia and single or multiple nucleoli. Few mitoses were observed. Within the nodules, several dilated vascular structures were visible, some of which showing angiolymphatic invasion. The neoplastic cells were strongly immunoreactive for CD10 (commonly expressed in cRCC) and vimentin. By contrast, thyroid transcription factor- 1 (TTF-1), thyroglobulin and CK7 were not found in tumoral cells and this ruled out a primary tumor of the thyroid. On the grounds of the morphological and immunohistochemical findings, along with the patient’s medical history, a diagnosis of intrathyroid metastasis of cRCC was made. Contacting the patient’s relatives for more information about his renal disease, they revealed that the nephrectomy had been due to cRCC, which had been concealed from the patient. This clarification confirmed the histological diagnosis of thyroid metastasis of cRCC, on a background of micro- and macrofollicular colloidal goiter. The patient underwent a whole-body CT scan and bone scintigraphy that was negative for metastases. Therefore, being at low-risk and under hemodialytic treatment, the patient was sent for oncologic follow-up. Discussion and Conclusion: Many patients suffering from thyroid metastases present a local symptomatology which is not easy to distinguish from that caused by primary pathologies of the thyroid. In the case we described here, the difficulty of diagnosis was not only due to the rarity of this condition, but was also complicated by the lack of information about the cause of the previous nephrectomy. In secondary thyroid lesions, it is necessary to ensure the total eradication of the gland (even for suspected malignant pathology) in order to guarantee oncologic radicality and extend the patient’s survival