MON-520 How Does the American Joint Committee on Cancer 8(th)Edition Tumor, Node, Metastasis Staging System Perform in Patients Evaluated at a Major Middle Eastern Medical Center?

The American Joint Committee on Cancer (AJCC) Tumor Node Metastasis (TNM) Classification of Cancer 8(th) edition (AJCC8) was officially introduced in January 2018 as a replacement for the previous version (AJCC7). Validation studies using data obtained from large cancer registries in North America demonstrated the superiority of AJCC8 over AJCC7 for prediction of survival. Subsequent studies from Europe and East Asia have mostly shown similar findings. However, these data may not be generalizable to other parts of the world. In this first study from the Middle East (Saudi Arabia), we compared these two versions of AJCC staging for their concordance and prediction of outcome in a large unselected sample of patients (pts) with DTC managed at a major referral medical center. We also compared the AJCC staging systems with the American Thyroid Association (ATA) Risk Classification. Of 814 consecutive pts seen during this period, 94 were excluded either due to their diagnosis being medullary or anaplastic thyroid cancer (37) or because of deficient data. The remaining 720 pts (149 males (20.7%), 571 females (79.3%) were included. The median age at the diagnosis was 37 yrs (range, 6-83). Total thyroidectomy was performed in 693 pts (96.3%) and central and/or lateral lymph node dissections in 487 pts (67.6%). I-131 was administered to 626 pts (87%). The tumors were classic PTC in 519 pts (72%), follicular variant PTC in 100 (13.9%), Tall cell PTC in 22 (3.1%), diffuse sclerosing PTC in 10 (1.4%), follicular thyroid cancer in 21 (2.9%) and other rare subtypes in 48 pts (6.8%). The number (%) of pts within each stage group by AJCC7 and AJCC8 respectively are as follows: Stage 1: 514 (71.4%) vs. 597 (82.9%), Stage 2: 46 (6.4%) vs. 75 (10.4%), Stage 3: 63 (8.8%) vs. 11 (1.5%), Stage 4: 97 (13.5%) vs. 37 (5.1%). Comparing AJCC8 with the ATA risk stratification system in 709 pts in which data were available, we found a high correlation with 96.8% of ATA low risk group being stage 1 in AJCC8, 2.9% stage 2 and 0.3% stage 3 and none in stage 4. The ATA intermediate risk group was 87.4% AJCC8 stage 1, 12.3% stage 2, 0.4% stage 3 and none in stage 4. The ATA high risk group was 19.1% in AJCC8 stage 1, 33% in stage 2, 9.6% in stage 3 and 38.3% in stage 4. In addition, AJCC8 was more predictive of the outcome with 80% of pts with evidence of disease (biochemically and structurally incomplete) being in AJCC8 stage 3 or 4 compared with 60% in AJCC7. For ATA staging, 8.6%, 22.4% and 67.7% of low, intermediate and high risk groups had evidence of disease at the last follow up, respectively. Conclusion: In this Middle Eastern population, AJCC8 downstaged a significant percentage of pts with DTC from higher stages in AJCC7. It also correlated better with the outcome and with the ATA risk classification system.