SUN-311 Anaplastic Thyroid Cancer After Liver Transplantation: A Case Report

Abstract Disclosure: G. Madrigal Loria: None. N.E. Fretes Oviedo: None. M.D. Lundholm: None. Background: Anaplastic thyroid cancer (ATC) is a rare, aggressive malignancy with a poor prognosis. Its occurrence post-liver transplantation is extremely rare, with limited cases reported. Post-transplant immunosuppression may contribute to oncogenesis, tumor dedifferentiation, and rapid progression, complicating diagnosis and treatment. Case Presentation: A 68-year-old male with Lynch syndrome, prostate cancer (cT1cN0M0, on active surveillance), and cholangiocarcinoma (pT2aN0M0) underwent deceased donor liver transplantation (DBD-OLT) four weeks prior and was on tacrolimus. He presented with progressive neck swelling, dysphagia, weight loss, low-grade fevers, and dyspnea. He had no family history of thyroid disease, and only an incidental 9-mm low-density left thyroid nodule preoperatively. On presentation, he had a firm, mobile mass in the left inferior neck. Laboratory results showed leukocytosis, mildly suppressed TSH (0.048 mIU/L), normal FT4/FT3, and negative thyroid peroxidase antibody and thyroid-stimulating immunoglobulin. CT imaging revealed thyroid enlargement, with the left thyroid nodule increasing to 17 mm over six weeks, accompanied by inflammatory changes and lymphadenopathy. Initial treatment with high-dose corticosteroids for suspected thyroiditis was ineffective. Given prior Candida infection, micafungin was started. Fine-needle aspiration (FNA) and core biopsy revealed anaplastic thyroid carcinoma (ATC), with tumor cells negative for BRAFV600E, NRAS, TTF-1, p40, SOX-10, desmin, and CD34. PET/CT demonstrated extensive metastasis to lymph nodes, lungs, pleura, newly transplanted liver, and bones. These abnormalities were new from pre-transplant pan-CT scans. Due to worsening airway obstruction from secretions, the patient had tracheostomy and nasogastric tube placement for tube feeds. Given the extensive disease burden, palliative radiation therapy was administered. The patient’s condition continued to rapidly decline, and medical oncology determined he was not a candidate for systemic cancer therapy. After discussions with his family, he was transitioned to home palliative care, where he passed away two weeks later. Conclusion: Anaplastic thyroid cancer following liver transplantation is exceptionally rare. This case highlights the highly aggressive nature of ATC, particularly in the setting of post-transplant immunosuppression. Given the exceptionally poor prognosis of ATC and limited therapeutic options in the post-transplant setting, further research is needed to better understand the incidence, risk factors, and optimal treatment strategies for this rare condition. Presentation: Sunday, July 13, 2025