Alpelisib + Fulvestrant + Metformin

The combination of alpelisib + fulvestrant + metformin represents a therapeutic approach for treating hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer with PIK3CA mutations. This combination includes alpelisib (a PI3K-alpha inhibitor), fulvestrant (an estrogen receptor antagonist), and metformin (an antidiabetic medication) used prophylactically to manage alpelisib-induced hyperglycemia. ## Mechanism and Clinical Use Alpelisib is a PI3K-alpha inhibitor that, when combined with fulvestrant, has demonstrated significant improvement in progression-free survival compared to fulvestrant alone in patients with HR-positive, HER2-negative advanced breast cancer with PIK3CA mutations[3]. The combination works by inhibiting the PI3K signaling pathway, which reduces tumor growth in xenograft models[5][6]. Hyperglycemia is a common adverse event associated with alpelisib treatment, occurring in up to 66% of patients in the SOLAR-1 trial[3]. This is an on-target effect that depends on the baseline metabolic status of the patient. Prophylactic use of metformin has been shown to decrease the rate and severity of hyperglycemia in patients receiving alpelisib[1][2]. ## Clinical Evidence The METALLICA trial investigated the prophylactic use of metformin in patients receiving alpelisib + fulvestrant. In this study, patients were stratified into risk groups for hyperglycemia (low, moderate, or high) based on baseline factors, and moderate and high-risk patients received prophylactic metformin[2][6]. The results showed that hyperglycemia adverse reactions occurred in 33% of patients with normal glycemic status and 70% of patients with impaired glycemic status, with Grade 3-4 hyperglycemia occurring in 2.1% and 15% of these groups, respectively[6]. A larger cohort study presented in 2024 included 139 patients treated with alpelisib + fulvestrant with a rational approach to metformin usage based on risk factors for hyperglycemia. Patients were stratified into low (47), moderate (46), and high (42) risk groups, with 3 patients having type 2 diabetes mellitus. Any grade hyperglycemia was reported in 62% of patients, with no cases of Grade 4 hyperglycemia detected. Grade 3 hyperglycemia was reported in 13% of patients, with 10% requiring alpelisib dose reduction and only 2% discontinuing alpelisib due to hyperglycemia[1]. ## Dosing and Administration The recommended dose of alpelisib is 300 mg once daily with food, while fulvestrant is administered at 500 mg intramuscularly on days 1, 15, and 29, and once monthly thereafter[4][5]. Metformin is typically started at least one week prior to alpelisib administration, with a starting dose of 500 mg twice daily, which can be increased up to 1,000 mg or 2,000 mg twice daily based on tolerability and risk group[2][6]. ## Adverse Events and Management Besides hyperglycemia, other common adverse events associated with this combination include rash, diarrhea, nausea, and vomiting. The incidence of gastrointestinal adverse reactions, including Grade 3 diarrhea, increases with metformin premedication[6]. Management of hyperglycemia typically involves dose interruptions or reductions of alpelisib, along with concomitant medications for hyperglycemia, which may include metformin, dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter-2 inhibitors, and sulfonylureas[3]. This combination therapy represents an important treatment option for patients with HR-positive, HER2-negative advanced breast cancer with PIK3CA mutations, with the addition of metformin helping to mitigate the hyperglycemic effects of alpelisib and potentially improving treatment adherence and outcomes.