This phase II, open-label, single-arm, study investigates the clinical benefit of everolimus combined with endocrine therapy (ET) in hormone receptor-positive (HR+), metastatic breast cancer (MBC) patients who progressed on prior PI3K inhibitor therapy (+ ET). The trial aims to determine if sequential inhibition of the PI3K/AKT/mTORC1 pathway retains efficacy post-PI3K inhibitor resistance, hypothesizing that everolimus will demonstrate a response rate exceeding the historical 9.5% observed in the BOLERO2 trial.