What factors aside from progression do you consider most important in determining whether a patient with metastatic papillary thyroid carcinoma is radioactive iodine refractory?

RAI refractory or resistant is defined as:

1. Progression despite adequate RAI RX within the prior year after therapy
2. Tumor that does not take up RAI either on a diagnostic or post-therapy whole body scan

If thyroglobulin is up and WBS is negative and positive LN on US, then the patient might be RAI-resistant.

I consider the following:

1. Progression within 6-12 months of RAI
2. Known disease without RAI avidity on appropriately stimulated I 123 or I 131 scan
3. Cumulative dose over 500 mci with documented progression

Several mutations/cytological subtypes, etc., are more likely to be non-RAI avid, including PDT...