Aggressive Behavior of an Underdiagnosed Tall-Cell Variant of Papillary Thyroid Carcinoma After Total Thyroidectomy and Radioactive I-131 Ablation

Abstract

Objectives: The tall-cell variant of papillary thyroid carcinoma (TCV-PTC) has been known for its aggressive biological behavior; however, this aggressive variant of PTC is usually underdiagnosed due to its rarity and difficult diagnosis, and there are no clinical features that can accurately diagnose it. Methods and Results: A 76-year-old African American man had an incidental finding of a thyroid nodule during a physical exam in 2007. A fine-needle aspiration (FNA) at that time showed follicular neoplasm with Hurthle cell changes. He subsequently underwent total thyroidectomy in 2008, followed by I-131 treatment. In 2017, he began having hemoptysis and an increase in thyroglobulin level. FDG-PET and CTA studies showed a density in the right lung, a 2.1-cm adrenal nodule, lesions in bones, and an anterior- midline neck mass with cervical lymphoadenopathy. The patient received I-131 ablation, but the lesion continued to grow. He presented to our hospital for the resection of the midline pretracheal neck mass in March 2018. Grossly, the mass weighed 56 g and measured 8.5 ± 4.6 ± 2.6 cm. Careful histopathological examination showed that >50% of the tumor cells were tall and fulfilled the previously mentioned diagnostic criteria for TCV-PTC. Follicular and solid/trabecular variants were also noted. Immunostains showed the tumor cells to be positive for TTF-1, PAX-8, and thyroglobulin but negative for Napsin-A. Conclusion: On tissue specimens, even small foci (<30%) of TCV-PTC should be mentioned, since the prognosis is usually worse in this patient population. Additionally, this case highlights the role of imaging modalities such as FDG-PET scanning, which have high sensitivity and accuracy to detect distant metastasis. The TCV-PTC patients are usually refractory to postoperative radioactive iodine treatment but may be susceptible to targeted treatments against BRAF mutations, which are usually present in the vast majority of TCV tumors.