Metformin is an anti-diabetic oral hypoglycemic agent that considered the gold standard therapy for the treatment of type 2 diabetes. Retrospective analyses show that metformin can offer therapeutic benefits to patients with several forms of cancer. It also has positive weight reducing effect on non-diabetic patient by improving insulin sensitivity (although the exact underlying pathomechanisms remain to be elucidated).

This prospective controlled study aimed to evaluate the effect of combined metformin adjuvant therapy and aromatase inhibitors (letrozole) in postmenopausal obese breast cancer women. In addition, to evaluate the effect of weight reduction on aromatase inhibitor efficacy.

Patients and methods: From February 2014 to June 2015, 75 Post-menopausal breast cancer females' patients were recruited, 53 patients underwent randomization and 45 patients completed six months, treatment. Aromatase inhibitor (letrozole) was administered as once daily in accordance to one of the three groups. Control group: fifteen obese females who received letrozole only; metformin group: fifteen obese females who received the same dose of letrozole plus metformin (2000 ± 500) mg daily, and lean group: fifteen non- obese breast cancer females who received letozole for six months, treatment period. Blood samples were collected at baseline and after six months of aromatase inhibitors treatment for analysis of serum estradiol, osteocalcin, insulin, leptin, lactate and glucose.

Inclusion Criteria:

• Postmenopausal women, postmenopausal is defined either by:

A. Age ≥ 55 years and one year or more of amenorrhea. B. Age < 55 years and one year or more of amenorrhea, with an estradiol assay < 20 pg/ml.

• Patients with breast cancer indicated for hormonal treatment with aromatase inhibitors (overweight 30 > BMI ≥ 25, obese BMI ≥ 30 kg/m2 and non obese BMI between 18 and 25 kg/m2).

Exclusion Criteria:

• • Diabetic patients.

  • Patients with metabolic syndrome.
  • Patients with last menstrual cycle less than one year ago.
  • Patient with conditions predispose to acidosis (heart failure, renal failure).
  • Ovarian radiation treatment with luteinizing hormone-releasing hormone (LH-RH) agonist (goserelin acetate or leuprolide acetate) is not permitted for induction of ovarian suppression.