Allostatic load and myosteatosis in women with metastatic breast cancer at diagnosis.

Abstract

e13018 Background: llostatic load (AL), a measure of cumulative physiological stress, and myosteatosis, fatty infiltration of skeletal muscle, have each independently been associated with adverse cancer outcomes. AL reflects chronic activation of stress-related physiological pathways that adversely affect multiple organ systems; therefore, it may represent an upstream contributor to alterations in body composition, including myosteatosis. However, few studies have assessed if AL correlates with myosteatosis. This study examined the association between high AL score and myosteatosis in women with newly diagnosed metastatic breast cancer (MBC). Methods: This cross-sectional study used data from a retrospective cohort study of women receiving care at an urban academic medical center (January 1, 2000-2024). Women aged ≥18 years with computed tomography (CT)-confirmed MBC and an L3 CT image at diagnosis were included. AL score was calculated using a definition from previous publications: a nine-biomarker composite score (range 0-9), with biomarker values outside established clinical thresholds assigned 1 point. The median AL score of the population was used to classify subjects as having high (≥2) or low AL ( < 2). Myosteatosis was defined using BMI-specific CT skeletal muscle radiodensity cutoffs ( < 41 HU for BMI < 24.9 kg/m2, < 33 HU for BMI ≥25 kg/m2). Spearman’s correlation and Fisher's Exact test were used to assess the association between high AL and myosteatosis in this MBC population. Results: In the analytic sample (n = 114), the mean (SD) age was 59.5 (13.2), the Caucasian population was most prevalent (46.5%, n = 53/114), the median (IQR) BMI was 29.4 (9.5), and the majority (62.3%) had high functional status at diagnosis (ECOG 0-1). The median (IQR) AL score was 2 (2) and 41.2% of women had high AL. The prevalence of myosteatosis was 46.5% (n = 53/114). No association was observed between AL score and skeletal muscle radiodensity (r = -0.036, p = 0.76). Chi-square analyses similarly demonstrated no association between AL and myosteatosis (p = 0.154). Conclusions: Among women with MBC, myosteatosis was moderately prevalent. However, no association was identified between AL score and myosteatosis at diagnosis. Further research with standardized definitions and longitudinal data is needed to clarify their independent and combined roles in prognosis of cancer outcomes.