Serum FSTL-1 and AI-assessed muscle parameters in cancer-related malnutrition.

OBJECTIVES: Follistatin-like protein-1 (FSTL-1) is emerging as a myokine linking skeletal and muscle biology. We investigated the relationship between circulating FSTL-1 levels and muscle mass and quality, using an artificial intelligence (AI)-enhanced ultrasonographic evaluation of the rectus femoris in patients with cancer-related disease-related malnutrition. METHODS: A total of 91 patients diagnosed with cancer and disease-related malnutrition were included in the study. Muscle mass assessment was performed through US evaluation of the rectus femoris, using an AI-based analytical ultrasound system. Complementary evaluations comprised BIA to determine skeletal muscle mass, appendicular skeletal muscle mass, and the appendicular skeletal muscle mass index, with determination of circulating FSTL-1 concentrations. RESULTS: Thirty-seven women and 54 men, with a mean age of 69.5 ± 10.6 years were enrolled. Sarcopenia was identified in 41 individuals (45.9%). Patients with sarcopenia showed significantly reduced values: body weight (-4.1 ± 1.0 kg; P = 0.02), calf circumference (-2.5 ± 0.3 cm; P = 0.03), phase angle (-0.7 ± 0.2°; P = 0.01), and reactance (-6.3 ± 1.3 Ω; P = 0.03), skeletal muscle mass (-2.3 ± 0.3 kg; P = 0.03), appendicular skeletal muscle mass (-3.7 ± 0.1 kg; P = 0.02), and appendicular skeletal muscle mass index (-1.3 ± 0.3 kg/m²; P = 0.02), cross-sectional area (-0.4 ± 0.2 cm²; P = 0.04), and y-axis (-0.27 ± 0.1 cm; P = 0.03), and pennation angle (-1.1 ± 0.2°; P = 0.02). Circulating levels of FSTL-1 were markedly reduced in patients with sarcopenia. In the multivariate logistic regression model, lower FSTL-1 concentrations remained significantly associated with an increased likelihood of sarcopenia (OR = 1.63, 95% CI: 1.10-4.21; P = 0.03. FSTL-1 demonstrated a moderate discriminative capacity for identifying sarcopenia, with an area under the receiver operating characteristic curve of 0.69 (95% CI: 0.51-0.73; P = 0.03). CONCLUSIONS: Reduced circulating FSTL-1 levels were independently associated with sarcopenia in patients with cancer-related malnutrition. These results indicate that FSTL-1 may act as a biomarker of impaired muscle quality and mass, as reflected by AI-assisted ultrasound and bioimpedance parameters.