Studying Changes in Breast Density in Patients With Early-Stage Breast Cancer Treated With Metformin Hydrochloride or Placebo on CAN-NCIC-MA.32

• Change in percent mammographic breast density in contralateral (unaffected) breast from baseline to 1 year using two-sample t-test or Wilcoxon rank-sum test [ Designated as safety issue: No ]
  

• Change in percent mammographic breast density in contralateral (unaffected) breast from baseline to 2 years using two-sample t-test [ Designated as safety issue: No ]
  
• Correlation between baseline mammographic density and baseline plasma fasting insulin, glucose levels, and HOMA using a scatter plot, correlation-coefficient estimation, and linear-regression method [ Designated as safety issue: No ]
  
• Correlation of changes in dense area in response to metformin therapy from pre-treatment to on treatment (at year 1 and year 2) with plasma fasting insulin, glucose levels, and HOMA using simple linear-regression method [ Designated as safety issue: No ]
  
• Correlation between mammographic density and the incidence of second primary breast cancer using correlation coefficient and scatter plot [ Designated as safety issue: No ]
  

OBJECTIVES:

Primary

• To evaluate the change in percent mammographic density in contralateral (unaffected breast) from prior to the initiation of metformin hydrochloride (metformin) or placebo treatment through one year of therapy in patients with hormone receptor-negative breast cancer (i.e., not on endocrine therapy).

Secondary

• To evaluate the change in percent breast density in contralateral (unaffected breast) from prior to the initiation of metformin or placebo treatment through two years of therapy in patients with hormone receptor-negative breast cancer (i.e., not on endocrine therapy).
• To evaluate whether baseline mammographic density correlates with baseline of fasting plasma insulin, glucose levels, and Homeostasis Model Assessment (HOMA) (collected on the treatment protocol CAN-NCIC-MA.32) (MA.32).
• To evaluate whether changes in dense area in response to metformin therapy from pre-treatment through two years of therapy correlate with changes in fasting plasma insulin, glucose levels, and HOMA (collected on the treatment protocol MA.32) over the same time period.
• To explore whether change in mammographic density for women on metformin is associated with risk of second primary breast cancer.

OUTLINE: Patients' mammograms taken at baseline and at approximately 1 and 2 years of metformin or placebo treatment are retrieved and analyzed for breast-density change. Pre-menopausal patients' menstrual cycle information is also collected at baseline and every 6 months for 2 years.