“…Changes in peripheral androgen and estrogen play an important role in the onset, recurrence and progression of the majority of breast cancers [ 39 ], and also in the pathophysiology of frailty syndrome [ 40 , 41 , 42 , 43 ], along with other factors such as inflammation and metabolic disorders [ 44 , 45 , 46 ]. The identification of biomarkers that could help clinicians to identify patients that develop frailty syndrome or suffer worsening of frail syndrome would facilitate clinical decision making and reduce adverse outcomes related to frailty [ 47 , 48 , 49 ]. As expected, during AROi treatment the concentration of estrogen in blood decreased due to aromatase inhibition [ 50 , 51 ], as evidenced in our study by the decrease in the aromatase activity index, the reduction of estrone (the main estrogen in postmenopausal women) [ 52 , 53 ] and the increase in androstenedione (the precursor of estrone) [ 53 , 54 ].…”