HIGH RATIO OF EARLY POSTOPERATIVE CALCITONIN TO PREOPERATIVE CALCITONIN COULD BE A NOVEL INDICATOR OF POOR PROGNOSIS IN PATIENTS WITH BIOCHEMICAL INCOMPLETE RESPONSES IN SPORADIC MEDULLARY THYROID CANCER

Objective: In a cohort of medullary thyroid cancer (MTC) patients with biochemical incomplete responses, 37 to 48% developed structural persistent disease; however, few indictors were available to distinguish those patients who were more likely to develop structural disease. We hypothesized that the relationship between preoperative calcitonin (Ctn) and postoperative Ctn (within 3 days after surgery) could be used to predict early prognosis of these patients. Methods: A total of 92 sporadic MTC patients were enrolled in this study. Our team proposed a novel indicator of structural persistent MTC called the calcitonin ratio (CR; CR = postoperative Cm/preoperative Ctn). Cox regression models and the Kaplan-Meier method were used to evaluate the prognostic capability of CR. The area under the time-dependent receiver-operating characteristic curves (AUC) and the Harrell concordance index (C-index) were used for analysis. Results: The cutoff CR value used to determine MTC prognosis was 0.15. Multivariate Cox analysis revealed that CR (hazard ratio [HR]: 22.974, 95% confidence interval [CI]: 3.259 to 161.959, P = .002), tumor-node-metastasis (HR: 3.968, 95% CI: 1.360 to 21.857; P = .031), and multi-focality (HR: 8.466, 95% CI: 1.286 to 55.716; P = .026) independently correlated with MTC prognosis. Kaplan-Meier survival curves demonstrated a lower proportion with structural persistent disease in patients with CR <0.15 (P<.001). The 3, 5, and 10-year AUC values were 0.798, 0.752, and 0.743, respectively. The C-index of CR was 0.788 (95% CI: 0.763 to 0.813). Conclusion: In this study, CR was identified as a sensitive and specific risk stratification marker for patients with biochemical incomplete responses in sporadic MTC.