The association between BMI and BRAFV600E mutation may differ by primary tumor size.

Objective: Previous reports suggest that a high body mass index (BMI) increases the risk of thyroid carcinoma. However, it remains unclear whether a high BMI is associated with the risk of BRAFV600E mutation. We aimed to assess whether a high BMI is associated with an increased risk of BRAFV600E mutation.

Design and methods: We screened 6,558 PTC patients who had undergone BRAFV600E mutation testing between January 2009 and December 2017. After exclusion, 6,438 PTC patients were enrolled. We used logistic regression, and restricted cubic spline plots of the adjusted odd ratios (ORs) were illustrated to model the relationship between BMI and BRAFV600E mutation.

Results: Among the 6,438 patients, 5,102 (79.2%) had the BRAFV600E mutation, and 4,954 (76.9%) were female. The median BMI was 23.8 (21.6 - 26.2) kg/m2. The primary tumor size was ≤ 1cm in 4,226 patients (65.6 %) and > 1cm in 2,212 patients (34.4 %). The BRAFV600E mutation was significantly associated with high BMI only in patients with primary tumor size > 1cm (OR 1.034; 95% CI 1.003 - 1.065; P = 0.029), whereas no clear association was found in patients with primary tumor size ≤ 1cm (OR 1.007; 95% CI 0.984 - 1.030; P = 0.570). Gender was not a significant factor in either group.

Conclusions: Our study found that a higher BMI was positively associated with BRAFV600E mutation in patients with primary tumor size > 1cm. These results suggest that the association between BMI and BRAFV600E mutation status differs depending on primary tumor size.