Endocrine Abstracts

Here we present a case of follicular thyroid cancer with elevation of thyroglobulin (Tg, in ng/ml) detected almost 10 years after initial surgery and radioactive iodine therapy (RAI). The elevated Tg persisted for years before he was found to have a metastasis in his kidney 16 years after his initial cancer treatment. A 78 year old male had a total thyroidectomy followed by RAI therapy in 2001 for a 2.4 cm follicular thyroid cancer. His Tg became mildly elevated in 2009, and continued to rise gradually. Body scan, PET scan and neck ultrasound did not find a source for the Tg. In 12/12 his Tg was 49.4 with a suppressed TSH. A thyrogen stimulated Tg in 2/13 was 930 and again ultrasound, body scan and PET scan were unremarkable. He was treated empirically with 210 mCi 131-I. His Tg level came down and remained <2 but a thyrogen stimulated Tg was 8.8 in 10/14. Tg antibodies have always been undetectable. Tg continued to rise to 96.5 on levothyroxine in 6/15. Again ultrasound, body scan and PET scan were unremarkable. On an abdominal CT scan for appendicitis in 10/15 a 1.4 cm right renal lesion was observed which remained stable on active surveillance. An increase in size of the renal mass was noted in Sept 2017 leading to radical nephrectomy. The pathology of the right kidney showed a lobulated 2.7×2.4×2.0 cm mass, and histologic appearance and immunostains led to diagnosis of metastatic thyroid follicular carcinoma. Tg in 3/17 on levothyroxine was 63.4, and rose to 95.4 in 6/17, 267.5 in 9/17 and 190.9 in 10/17 before his nephrectomy. Interestingly, the presence and change in the renal mass corresponded to his Tg levels all along. In retrospect the small renal mass could be seen on his PET CT films from 2012. The increased FDG uptake in the kidney appears to have been missed due to normal FDG uptake in the urinary tract. At the time of his last body scan in 2015 the renal mass was only 1.4 cm on CT and likely below the detection of the 131-I. A Tg level after kidney surgery is 1.1 Conclusion: Given the rarity of thyroid cancer metastases to the kidney, and the uptake of FDG in the urinary tract, a renal metastasis may be missed during evaluation of patients with persistent elevations of thyroglobulin.