Kwa M, et al. - The combination of exemestane with cyclophosphamide in patients with advanced HR-positive breast cancer was studied and changes in circulating immune cell subsets were determined. NoTreg depletion was demonstrated with low-dose cyclophosphamide when assessed by the specific marker, FOXP3 ⁺Helios⁺; however, baseline naïve Tregs were associated with 3-month progression-free survival (PFS). A favorable safety profile of the exemestane/cyclophosphamide combination was noted and provided evidence suggesting its clinical activity in heavily pretreated patients.