Papillary thyroid carcinomas (PTCA) are one of the most treatable cancers. Distant metastasis may occur, commonly to lungs and bones and is often associated with poorer prognosis. Metastasis to the thymus is extremely rare in any cancer and has only been reported in few case reports. We report a case of young Filipino patient presenting with papillary thyroid carcinoma metastasizing to the thymus. This is a case of a 32-year old Filipino female presenting with an incidental finding of a mediastinal mass with a palpable thyroid nodule. On neck ultrasound, multiple calcified nodules with increased vascularity over the right thyroid lobe and pretracheal lymphadenopathies were visualized. Fine-needle biopsy was performed and cytology was suspicious for PTCA. Chest CT showed non-enhancing hypodense cystic mediastinal mass while F18-FDG PET revealed a hypermetabolic thyroid nodule with a non-hypermetabolic right paratracheal mass. Total thyroidectomy with mediastinal mass excision was performed with histopathology showing PTCA metastasizing to perithyroidal and right thymic lymph nodes, left thymus and mediastinum. Radioactive iodine at a dose of 150 mCi was subsequently administered, followed by a post-therapy whole body scan showing no pathologic uptake. She was then maintained on TSH-suppressive dose of levothyroxine. On six months follow-up, TSH and thyroglobulin levels remained suppressed and a repeat neck ultrasound showed no evidence of recurrence. While PTCA is generally associated with a favorable prognosis, certain risk factors have been associated with worse clinical outcomes including advanced age, presence of distant metastasis and extent and size of the primary tumor. Age greatly affects the prognosis among PTCA patients as mortality was observed to be higher among patients aged 55 years above with distant metastasis compared to their younger counterparts. This provided the rationale for the current American Joint Committee on Cancer (AJCC) staging system which applies an age cut-off. In the recent years, it was also observed that while a younger age would lead to a better outcome in PTCA patients, certain young patients with distant metastasis still experienced poor survival outcomes compared to those without distant metastasis. Among these patients, male sex has been linked with poorer survival. Thymic metastasis in PTCA may be considered a distant metastasis. However, due to the scarcity of cases, the long-term clinical outcomes among PTCA patients with thymic metastasis is still uncertain. Few cases of thyroid malignancies with thymic metastasis have been reported and showed favorable prognosis with surgery alone. Nevertheless, due to an increased incidence of PTCA recurrence among Filipino patients, radioactive iodine therapy postoperatively was still performed for our patient in accordance to the American Thyroid Association (ATA) guidelines recommendation and led to favorable response. This highlights the importance of individualized management.
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