The thyroid cancer was papillary in 60%, follicular in 14%, and poorly differentiated in 25% of patients. Average cancer size was 37 mm. A total of 53% of patients had lymph node metastatic cancer foci. Spread of the cancer outside of the neck was present at diagnosis in 47% and otherwise was diagnosed during follow-up after an average of 3 years. Patients were considered resistant to radioactive iodine treatment because of lack of uptake in distant metastases, persistent metastases after high dose radioactive iodine treatment, or because of disease got worse despite persistent radioactive iodine uptake.
The average number of metastatic cancer foci per patient was 2, with an average maximum standard uptake value on PET-CT scan of 8.7, an average metabolic total volume of 3.7 cm3 and an average diameter of 16 mm. The average cancer growth rate was 41% per year. After an average follow-up of 77 weeks, 55% of patients died from thyroid cancer.
The metastatic cancer foci total growth rate did not correlate with maximum standard uptake value, metabolic total volume, or physical total volume. Among the four patients with five or more metastases, the cancers with the highest maximum standard uptake value or highest metabolic total volume did not have the highest tumor growth rate.
Overall 1- and 2-year-survival was 100% in patients with maximum standard uptake value <5. Survival was strongly correlated to patient cancer load as expressed as metabolic total volume or physical total volume.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
PET-CT scanning is a highly useful diagnostic tool for identifying metastatic disease. In patients with thyroid cancer that has spread and is resistant to radioactive iodine, uptake on a PET-CT scan was not predictive of the subsequent growth rate of the metastases as measured by CT scan 3 to 12 months after the initial PET-CT scan.
The present study confirms the correlation of total metabolic total volume with poor survival. The surprising finding was that the metastatic cancer foci with the highest uptake on PET-CT were not the metastatic cancer foci that grew the fastest. The apparent predictive power of metabolic total volume regarding survival may be due to the amount of cancer present rather than to the intensity of uptake on PET-CT scan.
— Ronald B. Kuppersmith, MD, FACS
ATA THYROID BROCHURE LINKS
Radioactive Iodine: https://www.thyroid.org/ radioactive-iodine/
Thyroid Cancer (Papillary and Follicular): https://www. thyroid.org/thyroid-cancer/