Inclusion Criteria:

- Ages 40 - 55 years

- Considered premenopausal or peri-menopausal

- Screening mammogram performed at Mayo Clinic Rochester within one year prior to the
current MBI study which demonstrates

- Negative/benign assessment (BIRADS category 1-2) or Additional imaging recommended
(BIRADS category 0), where the subsequent diagnostic workup results in a final
negative/benign assessment (BIRADS category 1-2).

- No proliferative benign lesions (e.g. fibroadenomas) identified

- Heterogeneously dense or extremely dense parenchyma (BIRADs density category 3 or 4)

- MBI performed less than 3 days prior to biopsy demonstrating either marked FD or
photopenic FD in an area of mammographically dense tissue amenable to biopsy.

- No use of exogenous hormonal drugs (e.g. hormonal contraceptives or sex steroid
hormones) within six months prior to study biopsy

- Negative pregnancy test or surgically sterilized (for patients in whom a study MBI
will be performed)

Exclusion criteria:

- Using any estrogen receptor modulating drugs (e.g., tamoxifen, raloxifene) or any
aromatase inhibitors within six months prior to study biopsy.

- Prior diagnosis of bilateral breast cancer.

- Diagnosis of breast cancer in either breast within 3 years prior to study MBI.

- Diagnosis of any cancer, except breast cancer (see #3) or non-melanomatous skin
cancer, for which patient has not been disease free for at least 5 years.

- Current breast symptoms

- Breast implants

- Known allergy to local anesthetic.

- History of bleeding complications from prior interventions

- Current use of anticoagulants (e.g., Coumadin or other blood thinners)

- Major medical condition