The concept of risk of recurrence stratification was first introduced in the 2009 ATA guidelines and updated in the 2015 ATA Guidelines. The risk of recurrence stratification was based on intraoperative pathologic features such as the extent of residual lesions, tumor size, pathologic subtypes, envelope invasion, degree of vascular invasion, lymph node metastasis features, molecular pathologic features, and Tg (sTg) levels after TSH stimulation (TSH >30 mU/L) and post-treatment whole body scan (Rx- WBS) and other weighting factors were used to classify patients into low, intermediate and high risk of recurrence.
This stratification system was used to guide whether to treat DTC patients with 131I.
1. Low risk of recurrence
PTC with all of the following: no distant metastases; all visual tumors were completely removed; tumors did not invade surrounding tissues; tumors were not aggressive histologic subtypes and did not invade blood vessels; if whole-body imaging was performed after 131I treatment, no iodine metastases were visualized outside the thyroid bed; a small number of lymph node metastases were combined (e.g., cN0, but pathologic examination revealed ≤5 micro-metastatic lymph nodes, i.e., metastases The maximum diameter of all metastases was ≤0.2 cm; follicular subtype of papillary thyroid cancer in the gland; differentiated follicular thyroid cancer in the gland with perineural invasion and with or without minor vascular invasion (<4 sites); micro papillary thyroid cancer with or without multiple foci and with or without BRAF V600E positivity were all classified as low risk stratification.
2. Intermediate risk stratification
Any one of the following: microscopic invasion of soft tissue outside the thyroid gland; invasive histology (e.g., high-cell, bootstrap, columnar cell carcinoma, etc.); papillary thyroid cancer with vascular invasion; iodine metastases in the neck on whole-body imaging after 131I treatment; lymph node metastasis (cN1, >5 metastatic lymph nodes on pathological examination, with metastases <3 cm in maximum diameter. BRAF V600E mutation-positive intraglandular papillary thyroid carcinoma (1-4 cm in diameter); BRAF V600E mutation-positive multifocal microscopic thyroid carcinoma with extraglandular infiltration.
3. High risk stratification
Any one of the following: significant extraglandular infiltration; incomplete resection of the cancer; confirmed distant metastases; high postoperative Tg levels suggestive of distant metastases; combined large lymph node metastases (any lymph node metastases ≧ 3 cm in diameter); extensive vascular invasion of thyroid follicular carcinoma (>4 vascular invasions)