We evaluated whether blood FGF21 concentration is associated with MS and its five criteria in postmenopausal women treated with AIs, and whether this persists after multimodal interventions that reduce MS.<h4>Methods</h4>A quasi-experimental longitudinal study in 31 postmenopausal women with localized BC on Ais, assessed via a 12-week multimodal program. Here, FGF21 is linked to breast cancer.