Abstract
Medullary thyroid carcinoma (MTC) accounts for 1.4% of all thyroid malignancies in Japan. Here, we studied the validity of a staging system evaluated preoperatively (Stage), intraoperatively (intra-Stage), and pathologically (pStage) based on the 6th and 7th UICC TNM classifications. One hundred and nineteen MTC patients who did not show distant metastasis at diagnosis and underwent locally curative surgery were enrolled in this study (average follow-up period: 173.4 months). Twenty-year clinical (not biochemical) disease-free survival (DFS) rates of Stage I, II, III, and IVA patients based on the 6th edition were 100, 88.2, 66.8, and 38.9%, respectively. DFS of Stage IVA patients was significantly poorer than that of Stage III patients (p = 0.03137). However, using the 7th edition, only 1 patient was classified with Stage III. Intra-Stage III patients based on the 6th edition showed a significantly poorer DFS (20-year DFS 50.0%) than intra-Stage II patients (92.9%) (p = 0.02668), and DFS of intra-Stage IVA patients (38.9%) tended to be poorer than that of intra-Stage III patients (p = 0.05439). Only one patient was classified with intra-Stage III using the 7th edition. In pStage, as many as 56 patients (47.1%) were classified with pStage IVA employing both editions. Taken together, Stage and intra-Stage were more useful to accurately discriminate high-risk patients than pStage, and their 6th editions were better than 7th editions. Although the number of patients was small, our data showed the possibility that intra-Stage in the 6th edition was the best staging system for MTC patients.
