Body Mass Index and Sporadic Medullary Thyroid Cancer: Insights from a Large Series

Background: Excess adipose tissue has been associated with the increased prevalence and aggressiveness of many human cancers. While its role in differentiated thyroid cancer is well established, in medullary thyroid cancer (MTC), data are conflicting. We aimed to evaluate the impact of excess adipose tissue on MTC prevalence, aggressiveness at diagnosis, and outcome in a large series of patients. Methods: We evaluated 529 patients with sporadic MTC from a prospectively maintained database. Weight and height were measured in all patients at the time of surgery, and body mass index (BMI) was calculated. Therefore, patients were classified according to BMI categories suggested by the WHO for Caucasian patients. Data about somatic mutations were available in 254/529 patients (48.0%). Results: The prevalence of subjects with obesity was higher than that in the Italian general population (20.2 vs. 12.0%). Patients with obesity presented smaller tumors, lower T and N stage, and lower AJCC 8th edition stage, as well as lower preoperative calcitonin values compared to under/normal and overweight ones. The prevalence of somatic RET and RAS mutations did not differ significantly across the WHO BMI categories. At the end of follow-up, structural disease was less common in patients with obesity (15.4%) compared to under/normal (25.6%, p < 0.05) and overweight (24.1%, p = 0.079). Further surgeries for local recurrence were less common in patients with obesity (3.8%) compared to overweight ones (11.0%, p < 0.05). Survival was superimposable in the different categories of BMI. Conclusions: Among patients with sporadic MTC, there is a higher prevalence of patients with obesity compared to the general population. A higher BMI was associated with less aggressive clinical presentation and better clinical outcomes.