Background: Medullary thyroid carcinoma (MTC) is rare. Nationwide population-based studies are important to evaluate its clinical course.
Objectives: To describe all patients with MTC in Norway during 1994-2016 and compare time-related trends in diagnostics and surgical treatment, including prognostic factors for biochemical cure and disease-specific survival (DSS).
Methods: This retrospective population-based cohort study includes data for 228 out of 237 patients (96%) with MTC; 201 patients were surgically treated. Patients were identified in the 4 regional centers treating MTC and by the Cancer Registry of Norway. Data were collected from patients' files. Trends were compared over 2 study periods.
Results: MTC accounted for 4.2% of thyroid carcinomas. During the study periods, the incidence increased from 0.18 to 0.25: 100,000 per year, preoperative diagnostics improved with increased use of calcitonin, ultrasound, and fine-needle cytology (p = 0.010, p < 0,001, and p = 0.001), patients were diagnosed at an earlier tumor stage (p = 0.004), and more patients were cured (p = 0.002). Via multivariate analysis of patients with metastatic lymph nodes, independent prognostic factors for cure were: a low ratio of metastatic and total number of dissected lymph nodes (p = 0.021) and no extrathyroidal extension (p = 0.030). Independent prognostic factors for DSS were: no distant metastasis, a younger age, and a low ratio of metastatic and dissected lymph nodes (p = 0.005, p = 0.020, p = 0.022).
Conclusions: Preoperative diagnostics have improved over time with increased therapeutic control. A low ratio of metastatic and dissected lymph nodes predicts better outcomes in patients with metastatic lymph nodes.
Keywords: Diagnostics; Medullary thyroid carcinoma; Outcome; Pathology; Surgery; Trends.