Association of Skeletal Muscle Mass and Muscle Quality at Diagnosis With Survival in Young Women With Breast Cancer: Retrospective Observational Study.

Background: Low skeletal muscle mass and poor muscle quality are associated with poor outcomes in women with breast cancer. However, gaps exist in our understanding of prognostic factors for young women (≤ 40 years), as they often have different body composition than older women. We evaluated pretreatment body composition measures in young women with breast cancer, including associations with overall survival (OS) and progression-free survival (PFS).

Methods: The Young Women's Database at Levine Cancer Institute was queried for women aged 18 to 40 at diagnosis (2009-2018) of single primary breast cancer (N = 870); patients with Stage 0 and 4 were excluded. Deceased patients with pretreatment computed tomography (CT) scans were identified (N = 40) and matched (1:1) to patients presumed alive by age, diagnosis year, and disease characteristics. CT-derived body composition measures included skeletal muscle index (SMI) and intramuscular adipose tissue corrected (IMAT-C). Sarcopenia (low muscle mass) was defined as SMI<40.

Results: Of 80 subjects, median age at diagnosis was 35 years. Median follow-up 8.6 years. Total 33% had low muscle mass (sarcopenic), and 56% had poor muscle quality (high IMAT-C). Independent of age, clinical disease stage, and primary insurer, high IMAT-C was associated with shorter PFS (HR 2.33, 95% CI 1.15-4.72; P = .020).

Conclusions: Poor muscle quality at diagnosis was associated with shorter progression-free survival in young women with breast cancer. Future research should determine the significance of changes in muscle quality throughout treatment.