Low skeletal muscle mass and strength are common in patients with metastatic breast cancer (mBC) and have been associated with treatment toxicities and poor prognosis. The PREFERABLE-EFFECT study (NCT04120298) investigated exercise effects on body composition, muscle strength, and functional performance (secondary outcomes) in patients with mBC.

Patients with mBC (n = 357) were randomized to a 9-month supervised aerobic, resistance and balance exercise program (EX) or control. Body composition (subset n = 66), lower body strength (subset n = 126), handgrip strength and functional performance were assessed at baseline, 3 and 6 months. Changes between groups were compared using linear mixed models for repeated measures.

EX significantly increased whole body lean mass at 3 months (between-group difference = 0.79 kg, 95%CI [0.14; 1.44], effect size = 0.14), appendicular skeletal muscle mass at 3 months (0.60 kg, [0.22; 0.97], ES = 0.19) and 6 months (0.48kg, [0.09; 0.87], ES = 0.15), and lower body strength at 3 months (18.32 kg, [7.58; 29.06], ES = 0.44) and 6 months (34.22 kg, [23.0; 45.45], ES = 0.83) compared to control. EX also improved functional performance, including balance, compared to control.

The results support the promotion of supervised exercise for patients with mBC, with beneficial effects on skeletal muscle mass, muscle strength and physical performance.

The PREFERABLE-EFFECT study was registered on ClinicalTrials.gov on October 9, 2019 (NCT04120298).