The purpose of this study is to see if Positron Emission Tomography (PET) imaging with a radioactive form of the hormone progesterone called FFNP will give the same results as hormone receptor testing already performed on tissue used to diagnose breast cancer.

Inclusion Criteria:

• Female patients 18 years of age or older
• Biopsy-proven breast cancer
• Tumor estrogen-receptor and progesterone-receptor status already determined or scheduled to be determined at time of surgery without intervening therapy.
• Primary lesion size ≥ 1.5 cm as determined by imaging studies (ultrasonography, mammography, CT or MRI) or physical examination
• Able to give informed consent
• Not currently pregnant or nursing: Subject must be surgically sterile (has had a documented bilateral oophorectomy and / or documented hysterectomy), post menopausal (cessation of menses for more than 1 year), non lactating, or of childbearing potential for whom a urine pregnancy test (with the test performed within the 24 hour period immediately prior to administration of FFNP) is negative.

Exclusion Criteria:

• No previous history of hormone therapy; NOTE - subjects who were treated with hormone therapy for reasons other than breast cancer or breast cancer prevention may be allowed to participate after review of history by the primary investigator
• Patients with other invasive malignancies, with the exception of non-melanoma skin cancer, who had (or have) any evidence of the other cancer present within the last 5 years
• Unable to tolerate 60-90 minutes of PET imaging per imaging session