Long-term outcome of medullary thyroid carcinoma in patients with normal postoperative medical imaging

Imaging-detected relapses are observed in a significant proportion of patients with medullary thyroid carcinoma (MTC) with normal postoperative imaging studies. The aim of this study was to search for prognostic factors of imaging-detected relapse. This retrospective study was performed in 63 consecutive MTC patients with normal postoperative medical imaging. After surgery, the basal calcitonin (CT) level was undetectable in 35 patients and elevated in 28. During follow-up, 18 patients developed a clinical or imaging-detected relapse (29%) in the neck and/or at distant sites: 15 had an elevated postoperative basal CT level and three had an undetectable postoperative basal CT level. At multivariate analysis, the significant parameters predictive of imaging-detected relapse were the postoperative plasma CT level and the tumour extension (pT). The 3- and 5-year relapse-free survival rates were 94 and 90% in patients with an undetectable postoperative basal CT level, and 78 and 61% in patients with a detectable basal CT level (P < 0.05). The 3- and 5-year relapse-free survival rates were 92 and 85% in the pT1-3 patients, and 57 and 46% in the pT4 patients (P < 0.01). These results show that postoperative CT level and tumour extension are critical prognostic factors for the identification of patients at a high risk of relapse.