['Low muscle mass (LMM) and low muscle attenuation (LMA) reflect low muscle quantity and low muscle quality, respectively. Both are associated with a poor outcome in several types of solid malignancies. This study determined the association of skeletal muscle measures with overall survival (OS) and time to next treatment (TNT).', 'A skeletal muscle index (SMI) in cm', 'The prevalence of LMM, sarcopenic obesity and LMA were 66.9%, 7.2% and 59.6% respectively. LMM and sarcopenic obesity showed no significant association with OS and TNT, whereas LMA was associated with both lower OS (HR 2.04, 95% CI 1.34-3.12, p\xa0=\xa00.001) and shorter TNT (HR 1.72, 95% CI 1.14-2.62, p\xa0=\xa00.010). Patients with LMA had a median OS and TNT of 15 and 8 months respectively, compared to 23 and 10 months in patients with normal MA.'] Is low muscle attenuation a prognostic factor for survival in metastatic breast cancer patients treated with first line palliative chemotherapy?