Myosteatosis at diagnosis is adversely associated with 2-year survival in women with estrogen receptor-negative metastatic breast cancer.

Purpose: To examine the relationship between skeletal muscle (SM) and cancer-specific outcomes for women with estrogen receptor-negative (ER-) metastatic breast cancer (MBC).

Methods: For this retrospective cohort, females (≥ 18 years) with histologically confirmed ER- MBC and computerized tomography (CT) imaging were screened. Demographic, anthropometric, and clinical data were collected uniformly from the electronic medical record. CT images inclusive of the third lumbar region (L3) at diagnosis, 6 and 12 months, were used to classify sarcopenia (≤ 41 cm/m) and myosteatosis (< 41 or 33 Hounsfield Units, adjusted for body mass index (BMI)) and to evaluate changes in SM and total adipose tissue (TAT) over time. Kaplan-Meier curves, Cox Proportional Hazards (PH), and restricted mean survival time (RMST) estimates were generated to examine the relationship between sarcopenia and myosteatosis and time to tumor progression (TTP), treatment toxicity and 2-year survival, adjusting for covariates.

Results: Participants were 58.0 (15.0) years of age, ethnically diverse (55% non-Hispanic white, 31% Black, 11% Hispanic), post-menopausal (73%, n = 111), and classified as overweight (BMI 29.4 (7.6)). At diagnosis, 40% (n = 61) were sarcopenic, 49% had myosteatosis, and 28% (n = 42) had both. While Cox PH modeling and RMST analysis reveal no significant relationship between sarcopenia at diagnosis and 2-year survival (RMST difference - 1.6 (1.4) months, HR 1.35 (0.88-2.08)), these analyses support a significant, adverse association between myosteatosis at diagnosis and 2-year survival (RMST difference - 2.4 (1.5) months, HR 1.72 (1.09-2.72)). Incident sarcopenia was 11% (n = 5/45) and 2.5% (n = 1/40), respectively, while incident myosteatosis was 19% (n = 8/42) and 15% (n = 5/34) at 6 and 12 months, respectively. TTP and treatment toxicities did not appear to be related to diagnostic SM or body composition changes over time.

Conclusion: Targeted interventions initiated within the first year of diagnosis to preserve or improve SM quality seem warranted for women with ER-MBC.