Endocrine Abstracts

Introduction

The term collision tumor refers to the coexistence of two histologically distinct malignant neoplasms. The two malignancies can originate from the same organ or occur as metastases from other regions. This type of tumors involving the thyroid gland are especially rare. Reported cases are usually involving papillary thyroid carcinomas in coexistence with other types of tumors like medullary carcinoma, follicular carcinoma or metastasic disease. Metastasic disease to the thyroid is uncommon but can develop after long-disease free intervals. Among the carcinomas metastasizing to the thyroid, renal cell carcinoma is one of the most frequent.

Case report

A 68-year-old man was referred to endocrinology due to a hyper metabolic focus in the upper pole of the thyroid lobe (Suv 3.7). He has a history of 6, 5 cm clear cell renal carcinoma with sarcomatous pattern. Right laparoscopic radical nephrectomy was performed six years ago. On physical examination, a soft multinodular goiter was palpable at the expense of the right thyroid lobe, and nodules were not delimited. The thyroid profile was in the normal range. A thyroid ultrasonography showed a 14 mm hypoechoic nodular image in the right thyroid lobe, not well defined, without increased vascularity. In addition a solid, hypoechoic nodule with irregular borders and an anteroposterior diameter of 11 mm was observed in the left thyroid lobe. USG-guided fine needle aspiration of the right thyroid lobe nodule was requested, which corresponded to the uptake observed on PET-CT. A pathology compatible with Bethesda II was obtained. Follow-up was carried out with laboratory tests and ultrasonography. In the control thyroid ultrasonography, a suspicious nodule with a greater craniocaudal diameter than anteroposterior and central and peripheral vascularization of 11 × 11 × 9 mm was observed in the upper pole of the right thyroid lobe. USG-guided fine needle aspiration was performed on said nodule, which was compatible with Bethesda III. Therefore, a total thyroidectomy was performed. Histologically, the thyroidectomy specimen revealed a 1.2 × 0.9 × 0.5 cm follicular thyroid carcinoma in the left thyroid lobe, as well as metastasis due to clear cell renal carcinoma in the right thyroid lobe.

Conclusion

This case report emphasizes that for any patient with a known history of malignant carcinoma, metastatic disease should be considered if new suspicious thyroid nodules appear. The role of pathological anatomy is important in the identification of collision tumors.