SAT-354 - A Rare Late Recurrence of Differentiated Thyroid Carcinoma with Bone Metastases in an Elderly Female

Introduction:
Differentiated thyroid carcinoma usually has excellent survival, with recurrence in up to 30% and distant metastases in only 5–10%, most often to lung and bone. Osseous disease may cause pain and hypercalcemia. After surgery, radioactive iodine remains a mainstay of systemic therapy in iodine-avid DTC, providing tumor control and improved progression-free survival. Late recurrence is defined as metastatic disease occurring more than 10 years after initial treatment. This is rare but clinically significant and often detected initially by rising thyroglobulin levels. We present an elderly patient with delayed recurrence of papillary thyroid carcinoma with metastatic disease to bone and lung more than a decade after hemithyroidectomy.

Case Presentation
We report an 82-year-old woman with follicular-variant papillary thyroid carcinoma treated with left hemithyroidectomy. She remained clinically stable on levothyroxine for twelve years until biochemical and radiographic evidence of disease recurrence emerged. Over three months of serial lab monitoring, thyroglobulin increased from 156.3 to 504.8 to 756.8 ng/mL, and calcium was mildly elevated at 10.4–10.6 mg/dL with persistently high parathyroid hormone (85–149.7 pg/mL). CT chest/abdomen/pelvis revealed a lytic lesion in the left iliac crest and a left lower lobe pulmonary nodule. She declined thyroidectomy, therefore suggested a 2 stage radioactive iodine ablation plan. First to ablate the thyroid, then the metastases. She completed the first stage with post-therapy PET-CT showing an FDG-avid lytic lesion in the left iliac bone, confirming metastatic disease. DEXA demonstrated osteoporosis of the bilateral femoral necks, left forearm, and lumbar spine. Persistent hypercalcemia with elevated PTH suggested primary hyperparathyroidism, possibly compounded by osteolytic metastasis. Despite her advanced age, she remained a candidate for further RAI, with plans for zoledronic acid therapy following ablation.

Conclusion:
This case highlights the importance of lifelong surveillance in thyroid cancer survivors, as metastatic recurrence may occur years after surgery. Rising thyroglobulin served as the earliest marker of disease progression. Elderly patients with iodine-avid metastatic disease may still benefit from RAI and require multidisciplinary care for bone metastases, hyperparathyroidism, and osteoporosis.

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