Table 1.

ATA 2009 Risk Stratification System with Proposed Modifications.²

Risk Level	Clinico-pathological Features
ATA Low Risk	Papillary Thyroid Cancer (with all of the following): No local or distant metastases All macroscopic tumor has been resected No tumor invasion of loco-regional tissues or structures The tumor does not have aggressive histology (e.g. tall cell, hobnail variant, columnar cell carcinoma) If 131I is given, there are no RAI avid metastatic foci outside the thyroid bed on the first post-treatment whole-body RAI scan No vascular invasion Clinical N0 or ≤5 pathologic N1 micrometastases (<0.2 cm in largest dimension)* Intrathyroidal, encapsulated follicular variant of papillary thyroid cancer* Intrathyroidal, well-differentiated follicular thyroid cancer with capsular invasion and no or minimal (<4 foci) vascular invasion* Intrathyroidal, papillary microcarcinoma, unifocal or multifocal, including V600E BRAF mutated (if known)*
ATA Intermediate Risk	Microscopic invasion of tumor into the perithyroidal soft tissues RAI avid metastatic foci in the neck on the first post-treatment whole-body RAI scan Aggressive histology (e.g. tall cell, hobnail variant, columnar cell carcinoma) Papillary thyroid cancer with vascular invasion Clinical N1 or >5 pathologic N1 with all involved lymph nodes <3 cm in largest dimension* Multifocal papillary microcarcinoma with extrathyroidal extension and V600E BRAF mutated (if known)*
ATA High Risk	Macroscopic invasion of tumor into the perithyroidal soft tissues (gross extrathyroidal extension) Incomplete tumor resection Distant metastases Postoperative serum thyroglobulin suggestive of distant metastases Pathologic N1 with any metastatic lymph node ≥3 in largest dimension* Follicular thyroid cancer with extensive vascular invasion (>4 foci of vascular invasion)*

Table from the ATA thyroid cancer guidelines.² Used with permission from the American Thyroid Association.

^*Proposed modifications, not present in the original 2009 initial risk stratification system.