ORIGINAL ARTICLE Associations between body mass index and clinico-pathological characteristics of papillary thyroid cancer Hye Jeong Kim*, Na Kyung Kim*, Ji Hun Choi*, Seo Young Sohn*, Se Won Kim*, Sang-Man Jin*, Hye Won Jang*, Sunghwan Suh*, Yong-Ki Min*, Jae Hoon Chung* and Sun Wook Kim* *Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, School of Medicine, Sungkyunkwan University, Seoul, Korea Summary Objective Epidemiological studies have demonstrated that excess weight increases the risk of thyroid cancer. However, the associations between excess weight and prognostic factors for thyroid cancer are uncertain. We evaluated the relationships between body mass index (BMI) and clinico-pathological fea- tures and outcomes of papillary thyroid cancer (PTC). Patients and Methods Retrospective analysis of 2057 patients with PTC was performed. Patients were grouped according to BMI (underweight, normal weight, overweight and obesity)- based World Health Organization standardized categories. Logis- tic regression models were used to assess the relationships between BMI and clinico-pathological features of PTC. A Cox proportional hazards model was used to examine the association between BMI and disease recurrence. Results A 5-kg/m 2 increase in BMI was associated with PTC tumours larger than 1 cm [odds ratio (OR) 131, P < 0001], with microscopic extrathyroidal invasion (OR 123, P = 0006), and with advanced tumour-node-metastasis (TNM) stage (OR, 130, P = 0003), which is independent of confounding variables such as gender, age, serum TSH, total cholesterol and fasting glucose level. The multivariate-adjusted OR [95% confidence intervals (CI)] in the overweight (250–299 kg/m 2 ) and obese (BMI  30) groups for tumours larger than 1 cm were 141 (110–181) and 217 (123–382), respectively, compared to the normal weight group (BMI 185–249). The multivariate- adjusted OR (95% CI) for microscopic extrathyroidal extension in the obesity group was 188 (106–332), and the OR for advanced TNM stage in the overweight group was 135 (102– 179) compared to the normal weight group. During follow-up (median, 84 month; range, 1–185), 43 patients (21%) experi- enced recurrence. There were no significant differences in recur- rence of PTCs among BMI groups. Conclusions Higher BMI was strongly associated with larger tumour size, extrathyroidal invasion and advanced TNM stage of PTCs. However, there was no difference in recurrence rate among BMI groups. This study suggests that excess weight is associated with aggressive features of PTCs. Further studies with long-term follow-up are needed to confirm this finding. (Received 29 March 2012; returned for revision 1 May 2012; finally revised 11 July 2012; accepted 16 July 2012) Introduction Over the past few decades, many countries have reported a rapid increase in the incidence of thyroid cancer, especially papillary thyroid cancer (PTC). 1 The increase can be partly attributed to increased detection of small cancers by the use of neck ultrasound and ultrasound-guided fine needle aspira- tion biopsies. Nevertheless, recent studies have found that the number of reported cases of PTC of all sizes and stages has increased over time, 2,3 suggesting that some environmental or other unknown factors might be involved in this phenome- non. Worldwide, the prevalence of obesity has also increased, 4 and epidemiological studies have shown that excess body weight, manifested in a higher body mass index (BMI), is associated with increased risk of thyroid cancer and other cancers such as oesophageal, colon and renal cancers in men and endometrial, gallbladder, oesophageal and renal cancers in women. 5–8 Little is known about the associations between BMI and clinico-pathological features or outcomes of thyroid cancer. Paes et al. 9 suggested that obesity may be correlated with less aggres- sive histological tumour features, such as the absence of nodal metastasis and tumour invasion. In contrast, Kim et al. 10 reported a positive association between BMI and advanced tumour stage, although their results did not reach statistical significance. Here, we sought to clarify the relationships among BMI, clinico-pathological features and prognosis (disease recurrence) in patients with PTCs in a relatively large cohort. Correspondence: Sun Wook Kim, Division of Endocrinology and Metab- olism, Samsung Medical Center, #50 Irwon-dong, Gangnam-gu, 135-710, Seoul, Korea. Tel.: (82)10 9933 1653; Fax: (82)2 3410 3849; E-mail: swkimmd@skku.edu 134 © 2012 Blackwell Publishing Ltd Clinical Endocrinology (2013) 78, 134–140 doi: 10.1111/j.1365-2265.2012.04506.x