Prognostic significance of neutrophil-to-lymphocyte ratio for long-term outcomes in patients with poorly differentiated thyroid cancer.

Poorly differentiated thyroid cancer (PDTC) is a distinct but rare type of thyroid cancer with intermediate biological behavior between differentiated and anaplastic thyroid cancers. PDTC was first defined in 2005 in Japan, but the diagnostic criteria changed in 2015, requiring the tumor to have more than 50% of poorly differentiated components for diagnosis. Because only six years have passed since the PDTC definition change, prognostic factors for long-term survival who meet the latest criteria have not been determined. Neutrophil-to-lymphocyte ratio (NLR) is a prognostic marker in various solid malignancies. However, its impact on PDTC remains unclear. This study aimed to evaluate the significance of NLR as a prognostic factor for patients with PDTC diagnosed based on the latest criteria. In total, 28 PDTC cases (4.4%) of 637 thyroid cancer patients who underwent surgery between 2002 and 2012 were retrospectively analyzed. The median follow-up period was 120 months (range, 7-216 months). Of the 13 deaths (46.4%), 9 patients (32.1%) died from PDTC. The median preoperative NLR was 2.7 (0.67-8.62), and the NLR cut-off value determined by the receiver operating characteristic curve was 2.88. Patients with a high NLR (>2.88) showed significantly worse disease-specific survival (hazard ratio [HR] 4.67, p = 0.036) and overall survival (HR 4.94, p = 0.007) than those with a low NLR (≤2.88). Multivariate analysis revealed that a high NLR independently predicted a worse prognosis (HR 6.06, p = 0.0087). In conclusion, NLR is a useful prognostic marker for patients with PDTC.