| Summary: | Background: Brown adipose tissue (BAT) has an essential role in regulating energy, metabolism, and thermogenesis in mammals. BAT activation is often detected in winter, especially in the female gender and in individuals with normal body mass index (BMI) by 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) modality. It has been reported to be associated with some factors such as age, plasma glucose, and outdoor temperature. Therefore, in this study, we aimed to investigate the characteristics of demographic, metabolic, and other variables of patients with FDG uptake in activated BAT on 18F-FDG PET/CT imaging in patients diagnosed with various types of cancer. Methods: 15752 patients diagnosed with various types of cancer who underwent whole-body 18F-FDG PET/CT imaging for routine diagnosis, staging, or follow-up between March 2017 and April 2019 were screened, and a total of 188 BAT-positive patients were included in this retrospective study. In addition to demographic patient characteristics such as age, height, and weight, data were collected such as BMI, date of birth, date and season of PET/CT imaging, laboratory findings, injection, and PET/CT imaging time, and the average outdoor temperature on the day of PET imaging and evaluated statistically. Results: A total of 188 BAT-positive patients (142 females [75.5%] and 46 males [24.5%]) were included in this study. The mean age of the patient group was 43.89 ± 13.67 years, and the mean BMI was 24.12 ± 3.56. About 103 patients (54.7%) with positive BAT were at normal weight (BMI 18.5–24.9), 49 patients (26.2%) were overweight (BMI 25–30), and 36 patients (19.1%) were obese (BMI >30). The injection time was 76.6% in the afternoon hours, whereas 77.1% of the imaging was performed in the afternoon hours. The mean fasting blood glucose (FBS) was 106.93 ± 14.28 mg/dl, and 61.7% (n = 116) of the patients were hyperglycemic. However, we found no significant relationship between BAT activation and the date of birth, place of birth, PET imaging season (relative to the northern hemisphere), and outdoor temperature. Conclusions: In our study, while BAT FDG uptake was not increased with cold exposure before PET scan and seasonally, female gender, younger age, and mean low BMI are the significant predictive value of BAT activation. Therefore, we aimed to emphasize that BAT activation should be considered to prevent the masking of the image and prevent false-positive involvement, especially in tumor tissue in risky groups.
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