Dynamic risk stratification in medullary thyroid carcinoma

Recently, dynamic risk stratification has been found to be more valuable than static anatomic staging system in nonmedullary thyroid cancer and this strategy has also been accepted in medullary thyroid cancer (MTC). The present study was designed to compare the clinical usefulness of response to initial therapy stratification with a traditional anatomic staging system. From August 1982 to December 2012, a total of 144MTC patients underwent thyroidectomy in Yonsei University Hospital. Among them, 117 (82.2%) patients with complete clinical data and sustained follow-up were enrolled in this study. Clinicopathological features and surgical outcomes were analyzed by retrospective medical chart review. Mean follow-up duration was 85.78±62.51 months. In this study, mean tumor size was 1.94±1.40cm and 22 (18.9%) patients had hereditary MTC; 95 (81.1%) patients had sporadic MTC. Stage I patients had highest probability of excellent response to initial therapy (92.1%). Stage IV patients had highest probability of biochemical and structural incomplete response to initial therapy (57.5% and 30.3%) and lowest probability of excellent response to initial therapy (12.1%). Both response to initial therapy stratification and TNM staging system offered useful prognostic information in this study. The TNM staging system provided risk stratification pertaining to disease-free survival (DFS), disease-specific survival (DSS), and the probability of having no evidence of disease at final outcome, but did not provide risk stratification pertaining to the probability of having biochemical persistent/recurrence disease at final outcome. However, response to initial therapy stratification provided risk stratification pertaining to not only DFS, DSS, and the probability of having no evidence of disease at final outcome but also the probability of having biochemical persistent/recurrence disease at final outcome. In this study, we demonstrated that dynamic risk stratification with adjusted response to initial therapy system can offer more useful prognostic information than anatomic staging system in MTC. Abbreviations: AJCC = American Joint Committee on Cancer, ATA = American Thyroid Association, CEA = carcinoembryonic antigen, CI = confidence interval, DFS = disease-free survival, DRS = Dynamic Risk Stratification, DSS = disease-specific survival, IAUC = Integrated Areas Under the Curves, LN = lymph node, MTC =medullary thyroid carcinoma, NED = no evidence of disease, NMTC = nonmedullary thyroid carcinoma, PVE = proportion of variance explained, ROC = receiver operating characteristic, TNM = tumor-node-metastasis, US = ultrasonography.