The Breast Cancer Personalized Nutrition (BREACPNT) study will evaluate the effect of a microbiome based personalized diet intervention on control of weight gain, glycemic response, disease outcome and various biomarkers in hormone receptor early breast cancer patients receiving adjuvant endocrine treatment.

Weight gain is a common incident in breast cancer survivors. As many as 50-96% of women experience weight gain during treatment. Endocrine treatment was identified as a risk factor for weight gain in several studies. Hence, weight management for breast cancer survivors is important for increasing adherence to therapy and lowering recurrence risk.

The essential role of the gut microbiota in modulating immune and metabolic functions in health and disease is increasingly recognized. Particularly in breast cancer (BC), diet plays an important role in creating a microbiome environment involved in estrogens metabolism. The microbiome directly affects the body's response to food.

The Personalized Nutrition Project, conducted in the Weizmann Institute of Science, showed that individuals vary greatly in their glycemic response to the same food, influenced by the involvement of functional microbial pathways. This study yielded an algorithm capable of accurately predicting personalized postprandial glycemic response (PPGR) to arbitrary meals. These results suggest that individually tailored dietary interventions help maintain normal blood glucose levels and influence microbiome diversity, which, in turn, can control weight changes.

In this phase 2 randomized trial, 200 Hormone receptor (HR) positive breast cancer patients, eligible for adjuvant endocrine therapy will be recruited to the study. Upon recruitment, subjects will provide a stool sample for microbiome analysis and will undergo continuous glucose monitoring for 2 weeks. Thereafter, patients will be randomly assigned in a 1:1 ratio to receive a personalized diet recommendation or a standard low-fat diet for 6 months. The algorithm is based on patients' microbiome analyses and other blood tests. Patient clinical records will be followed 2-3 times yearly for 5 years for DFS and BC recurrence.

Inclusion Criteria:

• Patients diagnosed with stage 1-3 breast cancer, who underwent surgery, have finished their neo/adjuvant chemotherapy and radiotherapy if these were indicated and are treated with adjuvant endocrine therapy (either Tamoxifen or Aromatase inhibitor +/- GNRH agonists).
• Patients are at least 60 days after finishing their last non-endocrine oncology treatment (i.e. definitive surgery, radiation or chemotherapy - whichever is last), have received at least 30 days of endocrine therapy ( tamoxifen or aromatase inhibitor) but no more than 24 months.
• Patients treated with neoadjuvant endocrine therapy are eligible provided they had undergone surgery, are least 60 days post their last non endocrine therapy (definitive surgery or radiation and chemotherapy, if these were indicated), are continuing their endocrine therapy but did not receive more than 24 months post-surgery.
• Are willing to work with smart phone application

Exclusion Criteria:

• Oral Antibiotics/antifungal use in the previous 3 months to profiling stage ( these patients will be able to join the study at a later point)
• Use of anti-diabetic and/or weight-loss medication
• BMI<18.5
• People under another diet regime and/or a dietitian consultation/another study?
• Pregnancy, breast feeding
• HIV carriers, Cushing syndrome, Chronic Kidney Disease, acromegaly, hyperthyroidism, liver cirrhosis
• Psychiatric disorders (Schizophrenia, Bipolar Disorder)
• Known diagnosis of IBD (inflammatory bowel diseases)
• Patients that underwent Bariatric surgery
• Known Alcohol or substance abuse
• Known Diagnosis of diabetes

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request .

12 months after publication

Formal request from qualified scientific and medical researchers on IPD and clinical study documents