Associations between body mass index and lymph node metastases of patients with papillary thyroid cancer

Epidemiological studies suggest that obesity is a risk of thyroid cancer, especially papillary thyroid cancer (PTC). However, the associations of obesity and clinic-pathological features, especially the association of body mass index (BMI) and lymph node metastasis of thyroid cancer are unclear. Seven hundred ninety-six primary patients with PTC were enrolled in this retrospective cohort study. The relationships between BMI and clinic-pathological features of PTC were evaluated by logistic regression models based on the 5-point increase in BMI and BMI quartiles (underweight, normal weight, overweight, and obesity). The 5-point increase in BMI was strongly associated with extra-thyroidal invasion [odds ratio (OR) 2.201, P < 0.001], primary tumor size larger than 1 cm (OR 1.267, P = 0.027), advanced tumor node metastasis (TNM) staging (OR 1.479, P = 0.004), and multifocality (OR 1.31, P = 0.01) in multivariable-adjusted models. The relationships between BMI and lymph node metastasis of PTC were evaluated by Mann-Whitney U test. The mean number of positive central lymph nodes and lateral nodes were increased with the increase of BMI when BMI ≥18.5 kg/m. It was not shown in underweight group. The present study found that increased BMI was associated with the lymph node metastases (LNMs) of patients with PTC, and other invasive features, including large tumor size, extra-thyroidal invasion, advanced TNM staging, and multifocality. Further studies with long-term follow-up are needed to confirm this finding.