Abstract
Introduction. This is an extremely rare case of a patient with metastatic follicular thyroid cancer who continued to produce thyroid hormone and was iodine scan positive without stimulation after thyroidectomy and radioiodine (I-131) therapy. Patient Findings. A 76-year-old Caucasian male was diagnosed with metastatic follicular thyroid carcinoma on lung nodule biopsy. Total thyroidectomy was performed and he was ablated with 160 mCi of I-131 after recombinant human thyrotropin (rhTSH) stimulation. Whole body scan (WBS) after treatment showed uptake in bilateral lungs, right sacrum, and pelvis. The thyroglobulin decreased from 2,063 to 965 four months after treatment but rapidly increased to 2,506 eleven months after I-131. Thyroid stimulating hormone (TSH) remained suppressed and free T4 remained elevated after I-131 therapy without thyroid hormone supplementation. He was treated with an additional 209 mCi with WBS findings positive in lung and pelvis. Despite I-131, new metastatic lesions were noted in the left thyroid bed and large destructive lesion to the first cervical vertebrae four months after the second I-131 dose. Conclusions. This case is exceptional because of its rarity and also due to the dissociation between tumor differentiation and aggressiveness. The metastatic lesions continued to secrete thyroid hormone and remained radioiodine avid with rapid progression after I-131 therapy.
Highlights
This is an extremely rare case of a patient with metastatic follicular thyroid cancer who continued to produce thyroid hormone and was iodine scan positive without stimulation after thyroidectomy and radioiodine (I-131) therapy
Ottevanger et al support the viewpoint that endogenous Thyroid stimulating hormone (TSH) stimulation may be responsible for enhancing the production of thyroid hormone by metastatic thyroid carcinoma [9]
They proposed that environmental causes, iodine deficiency, may play a role in thyroid hormone production by metastatic differentiated thyroid carcinoma
Summary
Follicular thyroid cancer (FTC) is the second most common type of thyroid malignancy worldwide after papillary thyroid cancer [1]. Thyroid cancer incidence has doubled since 1990 and it is estimated that 60,000 new cases will be diagnosed this year though the mortality rates remain stable [2] It is more prevalent in women and is usually diagnosed at an earlier age compared to other adult cancers [2]. The definitive diagnosis is a biopsy which helps to differentiate an adenoma from cancer [3] It may, in rare cases, present as metastatic disease mainly to the lung and bone; it can metastasize to other areas including the brain, liver, and skin [3]. Metastatic follicular cancer producing thyroid hormone remains extremely rare with only 47 cases reported from 1946 to 2005 as noted by Tardy et al [4]. A review of the literature on the possible explanation of hormone production by metastatic thyroid cancer and the factors involved in tumor metastasis follows the case presentation
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