SAT-357 - Delayed Subcutaneous Implantation of Papillary Thyroid Carcinoma Following Total Thyroidectomy

Introduction: Surveillance of papillary thyroid carcinoma (PTC) after treatment is dependent on risk stratification as well as response to initial therapy, with imaging deescalation after sustained excellent response. Recurrence is typically identified by rising thyroglobulin (Tg) levels or abnormalities on cervical neck ultrasound. Tumor implantation after diagnostic procedures, such as fine-needle aspiration (FNA), is a recognized but rare complication; however, implantation along a thyroidectomy surgical tract is uncommon and poorly characterized. Our case describes a patient in remission who presented 22 years post-total thyroidectomy and radioactive iodine (RAI) therapy with a subcutaneous lesion at the site of his surgical scar, highlighting an unusual mechanism of delayed recurrence.

Case Presentation: A 67-year-old man with history of PTC presented with a subcutaneous anterior neck lesion. On physical examination, the lesion was directly adjacent to the patient’s thyroidectomy surgical scar. The patient had total thyroidectomy and RAI ablation in 2003, with pathology showing 3.5 cm PTC, follicular variant (T2N0M0). Annual surveillance demonstrated repeatedly undetectable Tg and anti-thyroglobulin antibody (TgAb) concentrations, with normal thyroid ultrasounds. Patient was in structural and biochemical remission. Ultrasound of the subcutaneous lesion which appeared in 2025 demonstrated a 9 × 6 × 7 mm solid hypoechoic mass with internal vascularity. FNA demonstrated malignant cells consistent with thyroid origin (Bethesda VI). Immunohistochemical (IHC) staining was positive for Thyroid Transcription Factor-1 (TTF-1), Cytokeratin-7 (CK7), AE1/AE3 cytokeratins, and Tg. Serum Tg was repeated and found to be detectable at 0.8 ng/mL ( < 0.2 ng/mL). Whole-body nuclear medicine scan demonstrated focal uptake limited to the neck lesion, and PET/CT scan showed no evidence of metastatic disease. Stimulated Tg was 1 ng/mL ( < 1 ng/mL). Surgical excision was performed with negative margins. Pathology showed a 1.1 cm classical PTC with tall-cell features, involving the dermis and subcutaneous tissue. Patient remained under surveillance.

Discussion: This case adds to the scarce existing literature on thyroid carcinoma recurring as surgical tract implantation. Among fewer than 20 reported cases, our patient represents an exceptionally delayed presentation of surgically implanted tumor more than 2 decades after definitive treatment. New subcutaneous lesions at prior surgical sites warrant evaluation and clinicians should maintain a high index of suspicion even after decades of remission.

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