This clinical trial is focused on studying the effects of a medication called alpelisib on patients with a specific type of breast cancer known as metastatic breast cancer that is hormone receptor-positive and HER2-negative. This type of cancer has spread to other parts of the body and does not have an excess of the HER2 protein. The study will also involve a medication called fulvestrant, which is often used in combination with other treatments for this type of breast cancer. The trial aims to understand how the timing of taking alpelisib, along with fasting and a low carbohydrate diet, affects the side effects and effectiveness of the treatment.
The purpose of the study is to evaluate if there are differences in the occurrence of high blood sugar levels, known as hyperglycemia, when alpelisib is taken at night with a fasting period and a low carbohydrate diet, compared to taking it as usually recommended. The study will observe participants over a period of three months or until 30 days after they stop the treatment. Participants will be men and postmenopausal women who have a mutation in the PIK3CA gene and have experienced progression of their cancer after previous hormone therapy.
During the study, participants will be randomly assigned to different groups to receive the treatment at different times and under different dietary conditions. The study will monitor the incidence of severe hyperglycemia and other related outcomes. The goal is to determine the best way to administer alpelisib to minimize side effects and improve its effectiveness in treating this type of breast cancer.



Croatia