The PIK3CA gene is frequently mutated in breast cancer, leading to disease aggressiveness and patient mortality. Alpelisib, a small molecule that inhibits the activity of the PIK3CA gene product PI3K, has demonstrated clinical benefit in cancer patients with this gene mutation. However, hyperglycemia, an on-target toxicity associated with alpelisib that leads to hyperinsulinemia, limits the drug's clinical efficacy and induces high grade hyperglycemia in patients with baseline metabolic dysfunction, insulin resistance and/or elevated HbA1c. Restoring insulin sensitivity and reduction in circulating concentrations of insulin have been reported to improve the activity of alpelisib. Evexomostat (SDX-7320) is a polymer-conjugate of a novel small molecule methionine aminopeptidase 2 (MetAP2) inhibitor that has demonstrated the ability to reduce alpelisib-induced hyperglycemia in multiple animal experiments and has demonstrated synergistic anti-tumor activity independent of changes in glucose or insulin. Evexomostat was well tolerated in a Phase 1 safety study in late-stage cancer patients and showed improvements in insulin resistance for patients that presented with baseline elevated insulin. Overall, the most common treatment-emergent adverse events with evexomostat (TEAEs) were fatigue (44%), decreased appetite (38%), constipation and nausea (each 28%), and diarrhea (22%). All other TEAEs occurred at an incidence 20%. The purpose of this study is to characterize the safety of the triplet drug combination (alpelisib, fulvestrant plus evexomostat), to test whether evexomostat, when given in combination with alpelisib and fulvestrant will reduce the number and severity of hyperglycemic events and/or reduce the number of anti-diabetic medications needed to control the hyperglycemia for patients deemed at risk for alpelisib-induced hyperglycemia (baseline elevated HbA1c or well-controlled type 2 diabetes), and to assess preliminary anti-tumor efficacy and changes in key biomarkers and quality of life in this patient population.