Rethinking the Current AJCC Staging System for Medullary Thyroid Cancer: An Analysis of 3315 Patients
Presentation Number: OR22-3
Date of Presentation: April 2nd, 2016
Mohamed Abdelgadir Adam*1, Samantha Thomas2, Sanziana A Roman1 and Julie Ann Sosa3
1Duke University Medical Center, Durham, NC, 2Duke University, 3Duke University, Durham, NC
Considerable controversy exists around the American Joint Committee on Cancer (AJCC) staging system for medullary thyroid cancer (MTC). Our aim was to evaluate how well current AJCC (7thedition) stage groupings predict survival for patients with MTC, and to suggest a possible revision to sharpen estimates of prognosis.
MTC patients undergoing surgery were identified from the National Cancer Data Base (1998-2012). Patients with missing values for pathologic T, N, or M were excluded. Recursive partitioning was used to divide patients based on T, N, M stage into groups with similar overall survival (division criteria p≤0.01). Kaplan-Meier and adjusted survival analyses then were employed to examine survival differences among stage groups.
A total of 3315 patients were identified; 58% were female. Overall, 1223 (37%) patients had T1 tumors, 1098 (33%) T2, 562 (17%) T3, and 432 (13%) T4; 1910 (58%) N0, 560 (17%) N1a, and 845 (26%) N1b; and 165 (5%) M1. Based on the current AJCC staging, 941 (28%) patients had stage I, 907 (27%) stage II, 424 (13%) stage III, and 1043 (32%) stage IV tumors. In recursive partitioning analysis, four distinct TNM groups were identified based on within-group similarities in survival: group I (T1-2 N0 M0); II (T1-2 N1a-1b M0; T3 N0 M0); III (T4 N0-1b M0); and IV (T1-4 N0-1b M1). Differences in 10-year survival between TNM groups were more distinct among the newly created groups (86% for group I vs. 68% II vs. 48% III vs. 21% IV, log-rank p<0.0001) compared to the current AJCC stages (87% for stage I vs. 81% II vs. 72% III vs. 40% IV). After adjustment, survival differences across TNM groups were more distinct with the newly created TNM groupings (compared to group I, HR 3.06 for group II vs. HR 6.79 for III vs. HR 17.03 for IV), compared to the current AJCC staging (compared to stage I, HR 2.22 for stage II vs. HR 2.62 for III vs. HR 7.58 for IV). In the current AJCC system, compared to the newly created groupings, 2013 patients were upstaged, with 35% upstaged to stage II, 21% to stage III, and 44% to stage IV.
In this large analysis, the existing AJCC staging system for MTC appears to be less than optimal in discriminating risk of mortality among disease stage groups, with a significant number of patients upstaged to stage IV. Our results suggest that the current AJCC staging system could be improved with the newly identified TNM groupings suggested here for more accurate patient risk stratification and possibly treatment selection.
Disclosure: JAS: member of the Data Monitoring Committee of the Medullary Thyroid Cancer Registry, funded by Astra Zeneca, NovoNordisk, GlaxoSmithKline, and Eli Lilly., Member of the Data Monitoring Committee of the Medullary Thyroid Cancer Registry. Nothing to Disclose: MA, ST, SAR