ESA-SRB-AOTA 2019

Case Study: The clinical utility of Tg doubling time in the management RAI-Refractory follicular thyroid cancer. (#643)

Ayanthi Wijewardene 1 , Benjamin Kwan 1 2 , Robert Russo 3 , Bronwyn Crawford 1 2
  1. Department of Endocrinology, Concord Hospital, Concord, NSW, Australia
  2. Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
  3. Department of Nuclear Medicine, Concord Hospital, Sydney, NSW, Australia

Thyroid cancer guidelines recommend multi-tyrosine kinase inhibitors(TKI) for radioactive iodine (RAI)-refractory disease1,2. In clinical practice initiating TKI therapy remains contentious given significant treatment toxicity. We present a 69-year-old man who, in 2007, had a 30 mm follicular thyroid carcinoma abutting surgical margins and several foci of vascular invasion. A scan 6 months after RAI(3.7 GBq) showed no iodine-avid disease and stimulated Tg was undetectable. He was lost to follow up for five years.

In 2013, he represented with serum Tg 42.1 ug/L (TSH 2.24 mIU/L). A second dose of I-131(4.2 GBq) showed uptake in the thyroid bed only(stimulated Tg 110 ug/L). On suppressive  thyroxine Tg remained elevated (29 ug/L). In 2015, a third dose of I-131(4.0 GBq) showed no abnormal uptake (stimulated Tg 173 ug/L) and no FDG avid metastatic focus was seen on subsequent PET imaging.

In 2016 the suppressed Tg doubled in 6 months from 42 to 80 ug/L. Non-specific findings were seen on repeat FDG-PET imaging, including mild FDG avidity(SUV 3.2) at the L. pulmonary hilum and, on low dose CT, 5 subcentimetre nodules in L. lung. A diagnostic chest CT confirmed 5 small pulmonary nodules, 4-7 mm, with no hilar/mediastinal lymphadenopathy, which were not apparent following the fourth dose of I-131(6.2 GBq) . A Ga-68 Dotatate PET scan did not show octreotide avid disease.

Suppressed Tg level increased 10-fold(111 to 1122 ug/L) between Feb 2018 and May 2019. A progress CT chest showed 16 subcentimetre nodules throughout both lungs with a new hilar lymph node metastasis 28x23mm.  FDG-PET imaging showed marked FDG avidity at the L hilar mass(SUV 10.3) and several pulmonary nodules were FDG avid.

Although he remained asymptomatic(WHO performance score 0) Lenvatinib was commenced. Our case illustrates the clinical utility of Tg kinetics, in addition to imaging, as an objective measure to guide treatment.