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Introduction/Justification: Glucose intolerance is a metabolic abnormality recognized in patients with cancer cachexia and has been implicated in the development of low muscularity (LM). LM is an important feature associated with the poor prognosis of cancer patients, leading to a reduction in functional capacity, poor quality of life, increased treatment intolerance, and reduced overall survival. LM have been shown to correlate with insulin sensitivity. However, clinical studies evaluating the association between body composition features and insulin resistance are scarce, and the results are contradictory. Objectives: The purpose of this study was to evaluate the association between insulin sensitivity and the body composition features of patients recently diagnosed with rectal cancer. Materials and Methods: This is a cross-sectional study involving patients diagnosed with rectal cancer. Body composition was analyzed using computed tomography (CT) images processed with the SliceOmatic software based on the difference in tissue measurements by Hounsfield Units (HU). Muscularity was categorized according to Martin's criteria. Cachexia was categorized according to Fearon's criteria. Insulin sensitivity was evaluated using euglycemic hyperinsulinemic clamp. Personal information, tumor characteristics, and biochemical exams were collected from medical records. Statistical analyses were conducted using Stata Corp LP® version 17.0 software. This study was approved by the Institutional Review Board (CAAE: 91217418.2.0000.5404). Results: A total of 33 patients were included in the analysis. Low muscularity and cachexia diagnosis were identified in 27% of the sample (n = 9). The low muscularity (LM) group consisted mostly of females aged 55–70 years. There was no difference in BMI, weight loss, tumor stage, or ECOG score between muscularity groups. The LM group had a lower skeletal muscle area (p < 0.001), lower visceral adipose tissue area (p = 0.01), and there is no difference in skeletal muscle radiodensity (p = 0.85), subcutaneous adipose tissue area (p = 0.76), and intramuscular adipose tissue area (p = 0.46) when compared to normal muscularity group. A lower handgrip strength was also observed in the LM group (p < 0.01). Regarding insulin sensitivity, the LM group had a higher M-value adjusted for Free Fat Mass (FFM) (p = 0.01) and M-value adjusted for Total Body Weight (TBW) (p = 0.0347). Additionally, a significant negative correlation was found between muscularity and M-value-FFM (rho = -0.5047, p = 0.004) and M-value-TBW (rho = -0.4742, p = 0.0076). There was no difference in M-value between cachexia and non-cachexia patients. No statistical difference was observed in inflammatory markers (C-reactive protein, Glasgow prognostic score (mGPS), and neutrophil-to-lymphocyte ratio (NLR)) according to muscularity groups. Conclusion: There is no insulin resistance associated with LM or cachexia. It is possible that the main determinant of insulin sensitivity is the amount of visceral adipose tissue and systemic inflammation. The LM group exhibits a lower area of visceral adipose tissue, with no discernible difference in inflammatory markers. This study highlights the importance of expanding investigations into the determinants of metabolic changes and body composition in cancer cachexia.

Introduction/Justification: The assessment of skeletal muscle attenuation via computed tomography plays a crucial role in identifying myosteatosis among cancer patients. Myosteatosis, characterized by ectopic adipose tissue infiltration in skeletal muscles, has been linked to poor prognosis in various cancers. However, its implications specifically in rectal cancer remain uncertain. Studies have shown that myosteatosis correlates with increased insulin resistance, highlighting the need for further investigation in clinical settings. Objectives: This study aimed to investigate the relationship between insulin sensitivity and skeletal muscle radiodensity in patients recently diagnosed with rectal cancer. Materials and Methods: A cross-sectional study design was employed, inviting patients diagnosed with rectal cancer to participate. Insulin sensitivity was assessed using the M-value obtained from euglycemic hyperinsulinemic clamp tests. Skeletal muscle analysis was conducted using computed tomography (CT) images of the third lumbar vertebra processed with SliceOmatic software. Skeletal muscle was defined within the attenuation range of -29 to +150 Hounsfield Units (HU), while intermuscular adipose tissue was defined within -190 to -30 HU. The mean skeletal muscle radiodensity (SMR) was reported. Demographic and clinical data were collected from medical records. Statistical analyses were performed using Stata Corp LP® version 17.0 software. The study protocol received approval from the Institutional Review Board (CAAE: 91217418.2.0000.5404). Results: The analysis included a total of 33 patients, predominantly male (67%) with ages ranging from 55 to 70 years (58%). Patients across stages I to IV were represented, with 48% in stage III, 11% in stage I, 11% in stage II, and 30% in stage IV. Overweight and obesity were diagnosed in 37.5% and 30% of the sample, respectively. Common comorbidities included diabetes (21%), hypertension (60%), and dyslipidemia (21%). The M-value adjusted for Total Body Weight (TBW) demonstrated a significant association with Skeletal Muscle Radiodensity (rho = 0.3926, p = 0.0269), whereas no statistical difference was observed when adjusting for Free Fat Mass (FFM) (p = 0.1769). Conclusion: In conclusion, our findings suggest a moderate positive association between insulin sensitivity and skeletal muscle radiodensity in rectal cancer patients.