Body mass index in the evaluation of thyroid cancer risk.

BACKGROUND: Obesity has been linked to numerous diseases including thyroid cancer, but the exact nature of the relationship, especially with respect to patients with thyroid nodules, remains unclear. The objective of this study was to evaluate the impact of body mass index (BMI) on thyroid cancer risk in a population of patients with indeterminate cytology on fine-needle aspiration biopsy (FNAB).
METHODS: A total of 253 consecutive patients with indeterminate thyroid nodule FNABs who underwent total thyroidectomy in a tertiary care teaching hospital between 2002 and 2007 were reviewed. Height and weight reported on the anesthesia summary were recorded for each patient. Malignancy rates were calculated for the underweight, normal, overweight, and obese groups stratified according to their BMI. Subanalyses according to age and sex were also performed.
RESULTS: The risk of malignancy tended to be lower in obese patients compared to patients with BMIs in the underweight, normal, and overweight ranges (52% vs. 61%, p = 0.195). In men, a BMI classified as obese was associated with a significantly lower rate of malignancy (36% vs. 72%, p = 0.003). Women older than 45 years were a subgroup in which higher malignancy rates were associated with obesity (65% vs. 54%, p = 0.293). Conversely, in men over the age of 45 years and women under 45 years, a BMI in the obesity range was linked to a lower incidence of malignancy (20% vs. 68% p = 0.009 and 36% vs. 68% p = 0.043, respectively). When older women were excluded from the population studied, the rate of malignancy in obese patients was 36% versus 70% in nonobese patients (p = 0.002) with an associated reduction of 5% in the risk of malignancy per increased unit of BMI.
CONCLUSIONS: For patients with FNAB results of indeterminate significance, a higher BMI correlates with lower rates of thyroid malignancy for all patients except women over the age of 45 years.