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Breast cancer (BC) is a serious disease and is considered an important health problem worldwide. The prevalence of the disease in women according to Rosstat was 64,951 cases in the Russian Federation in 2020 (21.7% among all types of cancer).  Hormone-dependent estrogen receptor-positive (HR+), human epidermal growth factor receptor type 2 negative (HER2-) metastatic breast cancer (mBC) accounts for 70% of all cases.  About 40% of patients with ER+/HER2- mBC have mutations in the PIK3CA gene, leading to hyperactivation of the alpha isoform (p110α) of phosphatidylinositol 3-kinase (PI3K). Hormonal therapy with or without cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor is considered the standard treatment for patients with ER+/HER2- mBC. However, acquired resistance to this therapy remains a problem. Innovative methods for the treatment of breast cancer are the use of targeted therapeutic agents aimed at direct inhibition of the PI3K pathway in combination with hormone therapy. Alpelisib is a PI3Kα-specific inhibitor. Hyperglycemia is the most common side effect of alpelisib treatment. Currently, there is a consensus on the prevention and correction of hyperglycemia in patients receiving therapy with alpelisib, which recommends that before starting therapy, in  order to diagnose carbohydrate metabolism disorders and assess the risk of developing hyperglycemia, determine in all patients: the level of glycated hemoglobin (HbA1c), glucose fasting plasma (FPG), body mass index (BMI). And also to evaluate such risk factors as the presence of a family history of type 2 diabetes mellitus (DM 2), the presence of gestational diabetes in the patient's history, or the fact of the birth of children weighing more than 4 kilograms.Recently, new combinations of drugs have been actively used to treat disorders of carbohydrate metabolism, such as pioglitazone + metformin. This paper discusses the mechanism of action of PI3K inhibitors, new therapeutic combinations and their undesirable effects, and presents therapeutic experience.