Everolimus, a sirolimus (formerly called rapamycin) derivative, inhibits phosphatidylinositol 3-kinase (PI3K)/Akt/(158)mammalian target of rapamycin (mTOR) signaling pathway, which is one of the mechanisms of endocrine resistance in HR-positive breast cancer [157, 158]. The gene discussed is MTOR; the disease is breast cancer.