Obesity is a known risk factor for several cancers, including breast, colon, esophagus, kidney, uterus, and thyroid. Recent studies have reported that higher body mass index (BMI) is also associated with more advanced stage. The aim of this study was to investigate the clinicopathological relevance between BMI and papillary thyroid carcinoma (PTC).

A total of 798 patients surgically treated for PTC from January 2006 to June 2010 were included in this study. Medical records and pathologic reports were reviewed retrospectively. According to BMI, patients were divided into four groups: underweight (3.1%), normal (57.3%), overweight (31.6%), and obese (8.0%). Clinicopathological factors were analyzed and compared between normal and other groups.

According to the results, 709 patients were women (89.0%) and mean age was 48.5 years; mean follow-up period was 1,721±464.2 days. In comparison between the normal and underweight groups, there was significantly more extra-thyroidal invasion [Odds ratio (OR) 3.923, P=0.006] in the underweight group. In the obese group, tumor size was significantly larger (OR 1.794, P=0.007). However, there was no significant difference between the normal and overweight group.

In the obese group, tumor size was the only clinical significant factor between high BMI and PTC. Interestingly, more extra-thyroidal invasion was seen in the underweight group. To confirm this result, further studies with long-term follow-up and more patients are required.