MON-325 - Prioritizing Quality of Life in RAI-Refractory Papillary Thyroid Carcinoma: A Case of Aggressive Cutaneous Metastasis and Biochemical Progression

Introduction:
Metastatic papillary thyroid carcinoma (PTC) typically involves cervical lymph nodes, lungs, and bone. Cutaneous metastasis is an exceedingly rare presentation ( < 2% of cases) and often signals a high-grade transformation and a poorer prognosis.

Clinical

Case:
A 68-year-old female with a history of PTC underwent total thyroidectomy in 2011, followed by two rounds of radioactive iodine (RAI) therapy (50 mCi and 100 mCi) for pulmonary metastases. In 2019, she developed enlarging skin lesions on the right chest wall. Biopsy confirmed metastatic high-grade differentiated thyroid carcinoma with a papillary phenotype and a high mitotic count (9 mitoses/2 mm²).
Since the diagnosis of cutaneous recurrence, the patient has been on routine surveillance with PET scans and biochemical markers every 4 months without targeted therapy. Although PET scans have remained stable, the patient demonstrated significant biochemical progression despite consistent TSH suppression. Serial monitoring showed Thyroglobulin (Tg) rose from 30.1 ng/mL (SI: 30.1 µg/L) in March 2021 to 457.0 ng/mL (SI: 457.0 µg/L) by October 2024. Thyroglobulin Antibodies (TgAb) remained consistently undetectable ( < 0.9 IU/mL). This rapid Tg doubling time, in the context of previous RAI therapy, confirms aggressive, RAI-refractory disease.

Clinical Lessons:
Clinical Vigilance: Any new or growing skin nodule in a patient with a history of thyroid cancer must be biopsied; cutaneous metastasis is a rare but significant marker of disease dedifferentiation.
Prognostic Indicators: A high mitotic count (e.g. 5 per 2 mm²) in metastatic PTC suggests a high-grade variant with a higher risk of RAI refractoriness.
Quality of Life: In the setting of "biochemical escape" with stable imaging, management should prioritize the patient’s quality of life. Deferring systemic therapy is a proactive clinical choice in asymptomatic patients to avoid treatment-related morbidity.

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