Poster Presentation ESA-SRB Conference 2015

Treatment Resistant Papillary Thyroid Cancer (#237)

Jaime Lin 1 2 , Tien-Ming Hng 1 2
  1. Blacktown/Mt Druitt Hospital, Western Sydney Local Health District, Blacktown, NSW, Australia
  2. University of Western Sydney, School of Medicine, NSW, Australia

Synopsis

Investigations for TSH elevation revealed a mulitnodular goitre.  Progress ultrasound suggested malignancy and a follicular neoplasm was confirmed on biopsy. A total thyroidectomy was followed by radioactive iodine (RAI) ablation.  Histopathology revealed papillary thyroid cancer (insular variant) with extensive capsular and vascular invasion.

Uptake in the T1 and L2 vertebrae was noted post therapy. Further RAI was administered but thyroglobulin remained elevated (1380 mcg/L). Resection of metastatic T1 and L2 lesions were undertaken. A 3rd dose of RAI was administered and thyroglobulin levels measured 1089 mcg/L pre-treatment. Thyroglobulin levels continued to rise (2252mcg/L prior to 4th RAI treatment), with new lung and recurrent bone metastases developing. Selected lesions were 18 FDG-PET positive. Due to a paucity treatment options, a 5th RAI dose was administered (total dose of 21.6GBq). External beam radiotherapy was delivered to the T1 lesion.

Discussion

RAI resistance occurs when there is (1) no uptake on post therapy scan, (2) progression of disease and (3) rising thyroglobulin1. Although the metastases appeared iodine avid in this case, anatomical and biochemical response was lacking. These lesions corresponded to FDG-PET, reflecting a mixture of well and less well differentiated cell types.

The optimum I131 dose to treat metastatic disease remains unclear.  Higher doses are used when increased risk is perceived based on clinical and histopathological features2.  This dose can range between 3.7-7.4Gbq2 but data addressing the optimal therapeutic and safe accumulative dose is lacking.  Secondary malignancies have been associated with RAI therapy and are dose dependent3.  A meta-analysis has shown a 1.19 relative risk of secondary malignancies in patients receiving treatment for TC4. 

Tyrosine kinase inhibitors are currently being investigated and used as treatment for iodine refractory TC. However, access to these drugs in Australia is limited and if available, occurs in the setting of clinical trials.