Background: Follicular thyroid carcinoma (FTC) is a type of thyroid cancer that arises from the follicular cells of the thyroid gland. It accounts for about 10%-15% of all thyroid cancers. CA 125 is a protein that is often used as a tumor marker for ovarian cancer, but it can also be elevated in other types of cancers, including thyroid cancer. The significance of raised CA 125 levels in FTC is not clear, but it indicates a more advanced or aggressive form of the disease [1,2]. Case Presentation: A 62-year-old male presented with a painless neck mass (Figure 1) for 8 years. Ultrasonography revealed a solid nodule in the left lobe of the thyroid gland. Fine-needle aspiration cytology of the nodule showed features of follicular neoplasm. Contrast-enhanced computed tomography (CECT) abdomen and blood routine ruled out other causes of raised CA 125. Chest X ray and CECT neck (Figure 2) and thorax showed lung (Figure 3) and thoracic vertebra metastasis (Figure 5). Total thyroidectomy with bilateral central compartment lymph node dissection was performed. Histopathology confirmed FTC (Figure 4) with capsular invasion, and lymphovascular and perineural invasion and lymph node-positive. The tumor was classified as T3bN1a according to the tumor, nodes, and metastasis staging system. I131 scan post-surgery showed uptake in lung metastasis sites which confirmed the diagnosis. Conclusion: The role of serum tumor markers, such as CA 125, in predicting the prognosis of FTC is not well established. However, elevated CA 125 levels have been reported in some cases of thyroid carcinoma with metastasis, and may reflect the presence of peritoneal or pleural involvement [3,4]. This case highlights the aggressive nature of FTC with metastasis and the limited treatment options available for patients with advanced disease. CA 125 as a prognostic marker in FTC warrants further investigation [5].

Keywords: Follicular neoplasm, lung metastasis, CA 125.