Obesity has an important role in the pathogenesis of cancer; however, there are no clear mechanisms explaining the association between obesity and risk of thyroid cancer (TC).

It is a cross-sectional study including 184 patients with benign thyroid nodules (BN) and 19 patients with TC. Body mass index (BMI), waist circumference (WC), hip circumference (HC), waist/hip (W/H) ratio were assessed and correlated to relevant clinico-pathological features of the patients, different ultra-sonographic (U/S) criteria and risk of malignancy.

There was a significant increase in BMI, WC and W/H ratio in TC patients compared to BN group (P=0.001, 0.011 and 0.003). Increased BMI, WC and HC were associated significantly with solid nodules (P<0.05). WC increased in hypoechoic (103.1±15.4cm) and heterogeneous (103.8±16.7cm) nodules, compared to isoechoic (97.3±15.5cm) and hyperechoic (96.1±10cm) nodules (P=0.046). It also increased with lymph nodes enlargement (P=0.04). There was a significant association between WC and TIRADS classification (P=0.032), as it increased with TR4b (118.5 ± 12.9 cm) and TR5 (117.3 ± 13.9 cm) compared to TR2 (114.1 ± 15.7 cm, P=0.025 and 0.008, respectively). WC is an independent predictor for TC [OR: 1.092, CI: 1.020–1.170, P=0.012]. It achieved sensitivity, specificity and AUC (71.4%, 68.7% and 0.750; respectively), at a cutoff value of 108.5 cm (P=0.003), and when combined with BMI at a cutoff value of 32.59 (77.8% and 68.4%, respectively, AUC: 0.780, P<0.001).

Central adiposity is strongly associated with the risk of TC. WC is more superior to BMI when correlated with TIRADS classification and also is an independent predictor for TC.