In this study, positron emission tomography (PET/CT) imaging will be used to evaluate sigma-2 (σ2) receptor activity in sites of primary breast cancer using the investigational radiotracer [18F]ISO-1.

This study will evaluate the feasibility of using [18F]ISO-1 PET/CT to image sigma-2 receptor binding in primary breast tumors and continue to evaluate the safety of the tracer in this patient population. [18F]ISO-1 uptake measures will be correlated with qualitative immunohistochemical staining for cell proliferation (Ki67). This is an observational study in that [18F]ISO-1 PET/CT will not be used to direct treatment decisions.

Inclusion Criteria:

1. Adult patients, at least 18 years of age
2. Known or suspected breast cancer with at least one breast lesion that is 1 cm or greater in size by standard imaging (e.g. mammography, ultrasound or breast MRI)
3. Participants must be informed of the investigational nature of this study and provide written informed consent in accordance with institutional and federal guidelines prior to study-specific procedures

Exclusion Criteria:

1. Females who are pregnant at the time of screening will not be eligible for this study, urine or serum pregnancy test will be performed in women of child-bearing potential at the time of screening.
2. Inability to tolerate imaging procedure in the opinion of an investigator or treating physician
3. Serious or unstable medical or psychological conditions that, in the opinion of the investigator, would compromise the subject's safety or successful participation in the study.
4. Unwilling or unable to provide informed consent.