Brown adipose tissue activity on FDG PET/CT is associated with favorable change in lipid profile and reduced risk of diabetes

438 Objectives: Brown adipose tissue (BAT) plays a key role in energy homeostasis, conferring protection against diet-induced obesity, and has even been suggested as a potential target for the treatment of obesity and metabolic syndrome. The purpose of this study was to compare the metabolic outcomes (lipid profile and diabetes) of patients with and without BAT activity on FDG PET/CT, which remains the golden standard for visualization of BAT. Methods: PET/CT exams from 1834 breast cancer patients were retrospectively reviewed for bilateral symmetric elongated FDG activity in the neck and chest, typical of BAT activation. Because the data set was imbalanced, and to account for temperature changes in the environment, patients with BAT activity and those who underwent PET/CT exams on the same day (but without BAT activity) were included in the study. Blood glucose levels, lipid profile and presence of diabetes at baseline (time of PET/CT exam) and last clinical follow-up (mean follow-up of 57 months) were recorded. After testing for normality, nonparametric comparison of the groups with and without BAT activity was done using Mann Whitney U-test. Development of diabetes was analyzed with respect to the other clinical variables using Cox proportional hazard model. Results: 1.1% (20/1834) of the patients who underwent PET/CT demonstrated BAT activation, and 119 patients were analyzed for comparison as the group without BAT activity. The group with BAT activity showed significantly lower age (mean 41.8 vs. 53.7, p<0.001), lower BMI (mean 22.0 vs. 23.6, p=0.049), lower blood glucose (mean 90.3 vs. 109.3, 0.029) and lower total cholesterol (mean 169.4 vs. 190.4, p=0.029) than the group without. At last clinical follow-up, the group with BAT activity showed little change in terms of triglyceride and total cholesterol levels, but increased HDL (mean 45.5 to 60.8) and decreased LDL (mean 115.5 to 85.6). Presence of BAT activity was the only statistically significant predictor variable for diabetes on Cox regression (p=0.014), with a hazard ratio of -9.007. Conclusions: Patients with BAT activity demonstrated the characteristic traits of lower age, BMI, blood glucose and total cholesterol at baseline, and showed a favorable change in lipid profile on follow-up. The hazard for this group was also lower than for the group without BAT activity in terms of diabetes, further suggesting the role of brown fat in lipoprotein metabolism.