MON-395 - Papillary Thyroid Carcinoma with Fibromatosis-Like Stroma: Clinical and Management Considerations

Background: Papillary thyroid carcinoma with fibromatosis-like stroma (PTC-FLS) is a rare histologic variant, accounting for approximately 0.03-0.5% of PTC cases. Due to its rarity, standardized management guidelines are lacking. We present a case of PTC-FLS to highlight its diagnostic challenges and therapeutic implications.

Clinical

Case: A 36-year-old pregnant woman presented with progressive anterior neck pressure, voice changes, and dyspnea with tight clothing, and was found on examination to have a palpable thyroid nodule. Ultrasound demonstrated a 5.5-cm right thyroid nodule (TI-RADS 4), and fine-needle aspiration (FNA) was consistent with Bethesda category V. Right hemithyroidectomy was recommended but deferred during the second trimester of pregnancy at the patient’s request. Follow-up ultrasound eight months later showed interval enlargement to 7.4 cm and new, mildly suspicious 2.1 cm left level II lymphadenopathy. Repeat FNA yielded Bethesda category V cytology. Preoperative laboratory evaluation demonstrated thyroid-stimulating hormone of 1.54 uIU/mL (0.45-4.5 uIU/mL), thyroglobulin of 19.1 ng/mL (1.5-38.5 ng/mL), and thyroglobulin antibody of < 1.0 IU/mL (0.0-0.9 IU/mL). A total thyroidectomy was attempted but aborted due to tumor adherence to the right internal jugular vein and mediastinal structures. Pathology demonstrated a 3.5-cm classical PTC associated with FLS comprising 40% of the tumor with stromal infiltration into adjacent skeletal muscle and no lymph node metastasis (0/1). Although postoperative CT imaging of the neck showed no residual disease, the patient underwent a second-look procedure to achieve complete resection, including central neck dissection and removal of FLS from multiple soft tissue compartments. Postoperatively, the patient recovered well and will undergo outpatient levothyroxine titration and evaluation for consideration of radioactive iodine therapy.

Conclusion: PTC-FLS presents significant diagnostic and therapeutic challenges. Complete surgical resection remains the primary treatment, though the mesenchymal component is typically resistant to radioactive iodine. The underlying pathophysiology remains poorly understood; however, hormone-dependent tumorigenesis may contribute to tumor growth, as approximately 30% of cases express estrogen receptors. This case adds to the limited literature on PTC-FLS and supports further investigation into its biologic behavior and optimal management.

References:
1. Toniato A, Brusoni M, Mirabella M, et al. Papillary thyroid carcinoma with fibromatosis-like stroma: a case report and review of the literature. BMC Endocr Disord. 2023;23(1):80.
2. Wu Z, Chu X, Fan S, Meng X, Xu C. Papillary thyroid carcinoma with fibromatosis-like stroma: A case report and review of the literature. Oncol Lett. 2013;5(1):215-217.

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