[18F-FDG] PET/CT monitoring of tissue-specific changes in cancer patients at risk for cachexia
Authors: Rentz Lauren , Malone Briauna , Pistilli Emidio 
Published: May 2023

Prior research has identified lower muscle tissue CT attenuation in patients impacted by cancer cachexia. CT attenuation is a measure of tissue radiodensity, which in muscle, reflects the degree of myocellular fat and intramuscular fat infiltration. In contrast, PET imaging captures glucose uptake as quantified by the standardized uptake value (SUV). Collectively, CT and PET may provide an opportunity to identify tissue-specific differences that are associated with unintentional weight loss. This study utilized [18F-FDG] PET/CT imaging at multiple timepoints in cancer patients to investigate how adipose tissue and skeletal muscle properties change following cancer diagnosis and treatment. We hypothesized that longitudinal changes in CT attenuation and SUV adipose tissue and muscle would be more profound in cachectic individuals. Eighty-four patients (57M, 27F; 63.3±9.6 years; BMI 27.4±5.3) with stage 2 or 3 non-small cell lung cancer were imaged before and after chemoradiation treatment (162±32 days between scans). Pre- to post-treatment weight change averaged -4.93% (±9.6) normalized to six months, with 41 patients experiencing cachexia (defined as 5% weight loss in ≤6 months). CT attenuation (HU) and mean SUV normalized to body mass index were compared pre- to post-treatment. Pre-treatment, CT attenuation was higher in the non-cachectic group for the gluteus maximus (p=0.0087) and pectoralis major (p=0.0479), but not the erector spinae or subcutaneous adipose tissue (SAT). SUV was higher pre-treatment in the cachectic group in the erector spinae (p=0.0103) and gluteus maximus (p=0.0035); no group differences in the pectoralis major or SAT. Pre- to post-treatment decreases in CT attenuation occurred only in the non-cachectic group of the pectoralis major (p<0.0001), despite no changes in either group in the erector spinae, gluteus maximus or SAT. Post-treatment increases in SUV were seen in the non-cachectic group only for the erector spinae (p=0.0075) and gluteus maximus (p=0.0209), and both groups for the pectoralis major (cachectic, p=0.0333; non-cachectic, p=0.0304). In contrast, post-treatment increases in SUV only occurred in the cachectic group (p=0.0057). Findings suggest that both CT and PET can provide differential value in monitoring cancer induced changes to non-malignant tissues; changes in tissue composition, quantified via CT, are not linear with changes in metabolism, measured via PET. Further, the PET/CT profiles of all muscle groups do not initially exist or change in the same manner, which may correspond to variability in fiber type composition or function. Pre-treatment evaluation of adipose and muscle properties using both PET and CT could be useful for stratifying vulnerability to unintentional weight loss, allowing for early application of exercise and nutritional interventions. This research was funded by NIAMS (R01AR079445; Pistilli) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.