The purpose of this randomized trial is to determine the superiority of utilizing radioactive seed localization (RSL) over wire-guided localization (WL) for palpable or non-palpable malignant lesions in patients undergoing breast conservation surgery (BCS).

Consented and eligible subjects will be randomized to either radioactive seed localization or wire localization and stratified by surgeon and invasive versus DCIS prior to localization. Subjects on both arms will undergo breast conservation surgery including surgical specimen removal. Specimens will be grossed according to standard of care procedures. Localization, breast conservation surgery, and post-operative appointments will follow standard of care guidelines. Surveys will be administered according to the study calendar to the radiologist, surgeon, pathologist, and subject for data collection.

Inclusion Criteria:

• Female
• 20 to 99 years of age
• Breast lesion necessitating image-guided excision
• Unifocal disease
• Breast-conservation candidate
• Biopsy-proven malignant breast lesion including by not limited to invasive ductal carcinoma, invasive lobular carcinoma, and ductal carcinoma in situ
• Signed written informed consent document by the subject and/or a LAR

Exclusion Criteria:

• Male
• Multifocal or multicentric disease
• Receiving neoadjuvant chemotherapy
• Pregnant or breastfeeding
• Locally advanced disease
• Breast conservation contraindication such as inability to receive whole breast radiation therapy, inability to tolerate localization procedure, inability to lay flat or prone for radiation, and undesirable tumor to breast ratio
• Prior breast cancer on ipsilateral side
• Unable or unwilling to adhere to post-localization instructions (e.g. timely seed removal)