Histology of Functional Density in Premenopausal Breast

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