Distant metastasis in medullary thyroid carcinoma: Clinical outcomes and implications of T stage

The eighth edition of the American Joint Committee on Cancer tumour, node, and metastasis staging system did not take T stage into consideration when evaluating Stage IV C medullary thyroid carcinoma (MTC) patients. The aim of this study is to investigate the clinical outcomes and implications of T stage in this population.Eligible patients from the Surveillance, Epidemiology, and End Results database and the Department of Thyroid Surgery in West China Hospital of Sichuan University and who were diagnosed with Stage IV C MTC were included in this study. The overall survival (OS), the cancer-specific survival (CSS), and the precise cause of MTC-induced death were analysed. The potential risk factors, including the T stage, in the OS and CSS were evaluated by univariate and multivariate Cox regression models.This retrospective study enroled 204 Stage IV C MTC patients. The 5- and 10-year OS rates were 31.8% and 17.1%, respectively, and the 5- and 10-year CSS rates were 40.4% and 22.5%, respectively. More importantly, the rates of MTC-induced death between primary or distant metastatic lesions in Stage IV C MTC patients were comparable in our institution. Additionally, the univariate and multivariate analyses demonstrated that the presence of an advanced T stage was an independent prognostic factor for both the OS (T4 vs. T1-T3, hazard ratio [HR]: 1.714, 95% confidence interval [CI]: 1.175-2.500, p = .005) and the CSS (T4 vs. T1-T3, HR: 1.848, 95% CI: 1.229-2.780, p = .003).To achieve a better risk stratification, further classification of Stage IV C MTC patients by the T stage may be preferable.