ATA Low Risk

Papillary thyroid cancer (with all of the following):

• Does not have local or distant metastases

• The entire macroscopic tumor has been resected

• It has no tumor invasion of loco-regional structures or tissues

• The tumor has no aggressive histology (high cell carcinoma, Hobnail variant, and columnar cell carcinoma)

• If I131 is administered, avid metastatic foci outside the thyroid bed should not be identified in the first post-treatment full-body thyroid scan

• Without vascular invasion

• cN0 or ≤5 pN1 micro-metastases (<0.2 cm in the largest dimension)

Papillary thyroid cancer of intra-thyroid follicular variant, encapsulated

Intra-thyroid well differentiated follicular thyroid cancer with capsular invasion and no or minimal vascular invasion (<4 foci)

Intra-thyroid, unifocal or multifocal papillary microcarcinoma, including mutated BRAF V600E (if known)

ATA Intermediate Risk

Microscopic invasion of the tumor to the peri-thyroid soft tissues

Avid metastatic foci of radioactive iodine in the neck at the first full-body scan post-treatment Aggressive histology (high cell carcinoma, Hobnail variant, and columnar cell carcinoma)

Papillary thyroid cancer with vascular invasion

cN1 or >5 pN1 with all lymph nodes affected <3 cm in greatest dimension Multifocal papillary microcarcinoma with extra thyroid extension and mutated BRAF V600E (if known)

ATA High Risk

Macroscopic invasion of peri-thyroid soft tissue tumor

Incomplete tumor resection

Distant metastasis

Postoperative serum thyroglobulin suggestive of distant metastases

pN1 with any metastatic lymph node ≥ 3 cm in greatest dimension

Follicular thyroid cancer with extensive vascular invasion (>4 foci of vascular invasion)