Superiority of metastatic lymph node ratio over number of node metastases and TNM/AJCC N classification in predicting cancer-specific survival in medullary thyroid cancer.

Background: In medullary thyroid cancer (MTC), it is unclear which nodal classification system, metastatic lymph node ratio (MLNR), number of node metastases, or TNM/AJCC N classification, predicts cancer-specific survival best.
Methods: Kaplan-Maier analysis of cancer-specific survival after operation at a tertiary center.
Results: Included were 505 MTC patients. The spread of the survival curves was greatest after stratification by MLNR (in 0.20 increments), followed by number of node metastases (in 10-node and 20-node increments) and TNM/AJCC classification (N0, N1a, N1b). After collapsing overlapping survival curves, all adjacent curves (MLNRs ≤0.20 vs. 0.21-0.60 vs. >0.60; 0 vs. 1-20 vs. >20 node metastases; and TNM/AJCC N classification N0/N1a vs. N1b) significantly differed between each other.
Conclusions: In MTC, MLNR, reflecting intensity of lymphatic spread, predicts cancer-specific survival better than number of node metastases or TNM/AJCC N classification. The applicability of these findings to patients with limited neck dissection requires more research.
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