If you agree to take part in this study, you will be assigned to one of two groups, depending on how long you have been receiving anastrozole treatment. If you are within two months prior to or one month after starting treatment, you will be assigned to Group 1 and you will be followed through 2 years of treatment. If you have been taking anastrozole for about 2 years, you will be assigned to Group 2 and you will be followed through your third year of treatment.