This study evaluates the efficacy of the probiotic food supplement Vivomixx in the prevention of bone loss occurring in post menopausal women with breast cancer treated with an aromatase inhibitor. Half of the participants will receive Vivomixx while the other half will receive a placebo. The primary endpoint is to assess changes of bone turnover markers during the period of 6 months.

Aromatase inhibitors function to reduce estrogen levels. They are considered first-line treatment for postmenopausal women with estrogen receptor-positive breast cancer. Estrogen depletion leads to significant loss of bone mineral density and an increased fracture risk. One contributing mechanism to "estrogen deficiency associated bone loss" is the increase in systemic and local gut inflammatory responses upon estrogen deficiency. Probiotics have been shown to decrease inflammatory cytokine formation in both the systemic circulation and gut.

Vivomixx is a high potency probiotic medical food designated for the dietary management of inflammatory gut conditions in adults and children and is currently being studied in clinical trials in a wide variety of inflammatory conditions such as asthma and diabetes. In preclinical studies Vivomixx has been shown to protect from estrogen deficient bone loss.

Inclusion criteria

1. Age≥ 35 years
2. Breast cancer stages 1-3 (non metastatic)
3. Under treatment with aromatase inhibitors
4. In menopausal status for ≤10y
5. Estrogen receptor positive tumor
6. CTX ≥300 pg/ml

Exclusion criteria

1. Distant metastases
2. Additional active primary malignancy
3. Metabolic bone disease (primary hyperparathyroidism, hyperthyroidism, paget, osteomalacia etc)
4. Glucocorticoid treatment (chronic or high dose >7.5 mg in the last three months)
5. Bisphosphonate treatment for more than 3 months in the last 2 years
6. Bone densitometry (DXA) T-Score <-2 unless not a candidate for antiresorptive therapy (unwilling/unable to take treatment)
7. Lactose intolerant subjects