Background: The clinical relevance of clearly defined pretherapeutic basal calcitonin (bCt) cut-offs for predicting lymph node metastases (LNMs) and long-term outcomes (LOs) has so far not been tested in a large cohort of patients with medullary thyroid cancer included in a Ct screening program during the initial diagnostic workup of thyroid nodules.
Material and methods: Female (f) patients with a bCt level of ≤23 pg/mL and male (m) patients with a level of ≤43 pg/mL were assigned to Group 1 (minimal oncologic risk), patients with a bCt between 24 and 84 pg/mL (f) and 44-99 pg/mL (m) to Group 2 (low oncologic risk), and those with a bCt of ≥85 pg/mL (f) and ≥100 pg/mL (m) to Group 3 (high oncologic risk). All patients underwent surgery applying a uniform surgical protocol. The median follow-up was 100 months.
Results: The study included 306 patients. In 3/115 (2.6%) patients in Group 1 and in 3/50 (6.0%) in Group 2, LNM in the central but not lateral neck and no distant metastases (DMet) were documented. In both groups, the biochemical long-term cure rate was 95.7% and the disease-specific-survival (DSS) rate was 100% at 10, 15 and 20 years. Lateral LNM and DMet were diagnosed only in Group 3. The bCt levels of N0 and N1 patients showed broadly overlapping ranges, thus impeding the differentiation between those patients through bCt. Both the cure rate and DSS were significantly worse in Group 3. The overall biochemical long-term cure rate was 78.2%.
Conclusions: Within a Ct screening program, grouping patients upon pretherapeutic bCt provides a simple risk classification system for indicating surgery, predicting LN involvement, and LOs.
Keywords: medullary thyroid carcinoma; oncologic risk stratification; pretherapeutic calcitonin cut-offs; prognosis.