Endocrine Abstracts

Introduction: Follicular thyroid carcinoma (FTC) is the second most common thyroid tumor and accounts for about 5-10 % of all thyroid cancers. As FTC often retains the ability to concentrate radioactive iodine (I¹³¹), tumor may be responsive to I¹³¹ therapy. However, about 60-70 % of all metastatic thyroid cancers are resistant to I¹³¹ and has a poor prognosis with 10-year survival rate of 10 % and the average life expectancy 3-5 years after diagnosis.

Case: A 64-year-old man was admitted to the Hospital of Lithuanian University of Health Sciences Kaunas Clinics for thyroidectomy due to thyroid follicular carcinoma pT3NxMx. Levothyroxine replacement therapy and I¹³¹ therapy were indicated. Four years later, patient was diagnosed with follicular thyroid carcinoma metastasis to the right III rib and S2-3 vertebra. Surgical treatment and I¹³¹ therapy were ineffective. After a few years, bone pain intensified, but ultrasonography (US) and computer tomography (CT) denied the possibility of relapse so the treatment with Denosumab was started. One year later, CT revealed a pathological lymph node between the right kidney and v. cava inferior - stereotactic radiation therapy was performed to the pathological lymph node. Patient complained about numbness in the buttocks, anal fissure, neck lump and weight loss.

Diagnostic tests: Chest, abdomen and pelvic organs CT: Pathological lymph node had increased up to 1,6 cm between the right kidney and v. cava inferior. A 6,7 cm solid mass was observed in the sacrum.

Thyroid US: A 2,2 x 1,3 x 2,6 cm of hypoechoic, non-homogeneous tissue with microcalcinates in the post-operative area was observed. There were no pathological lymph nodes in the neck.

Microscopic examination: : Biopsy of sacral solid mass identified follicular thyroid carcinoma metastasis. Fine needle aspiration biopsy of the neck lump revealed Hurthle cell neoplasia.

Treatment: Systemic treatment with Lenvatinib was initiated. A positive effect is observed after V courses of Lenvatinib, sacral and neck tumor masses have decreased. Lenvatinib has caused transient skin lesions and mild gastrointestinal disorders, treatment is continued.

Conclusion: Resistance to I¹³¹ is usually associated with higher mortality rate so that precise multiple imaging tests of the targeted organs with possible metastasis and molecular testing are important for appropriate management of the disease.