RATIONALE: It is now standard for most breast cancer patients with 1-2 positive sentinel nodes to avoid completion node dissection when eligibility criteria from the American College of Surgeons Oncology Group (ACOSOG) Z0011 trial are met. The National Comprehensive Cancer Network (NCCN) recently proposed to extend this indication to patients that present with biopsy proven node positive disease if only 1 or 2 suspicious nodes are found on imaging, these positive nodes are not palpable clinically, and the other eligibility criteria from the Z0011 study are otherwise met. However, this recommendation is based on an expert consensus and no study has yet confirmed the optimal method to stage the axilla in this patient population.

PURPOSE: Evaluate the technical success rate and accuracy of sentinel node biopsy (SNB) and the potential benefits of clipping and removing the biopsy proven node using radioactive seed localisation (RSL) (SNB+RSL = Targeted Axillary Dissection (TAD)) in patients with biopsy proven positive nodes, limited nodal disease in imaging and clinically negative axillary examination.

This is a prospective multicenter study. Patients with T1-2 Breast cancer and clinically negative axilla on palpation, 1-2 suspicious nodes on ultrasound, and a biopsy proven positive node (by core biopsy of fine needle aspiration) will have a radioactive seed (I125) placed in their clipped node before surgery. At the time of surgery, patients that are scheduled for breast conserving surgery or mastectomy will have sentinel node biopsy (SNB) using radioactive dye (Tc99) +/- blue dye as well as retrieval of the clipped node using radioactive seed localisation (RSL). Removal of the I125 radioactive seed in the clipped node will be performed before the Tc99 counts are performed to prevent "shine through" and biased measurements. Imaging of the surgical specimen will confirm retrieval of the clipped node. Prospectively recorded information on pre-operative axillary imaging, characteristics of the retrieved nodes in the operating room and detailed pathological analysis of each corresponding node will be performed. Completion node dissection (CND) is not mandatory in this study but recommended if the clipped positive node is not retrieved, if 4 nodes or more are positive or if 3 nodes are positive in the absence of axillary radiation. The benefits of adding RSL to SNB and the benefits of adding SNB to RSL staging of the axilla will be evaluated in this study and will help to better define the value of using TAD in this patient population.

Inclusion Criteria:

• Participants must be ≥ 18 years old.
• Participants with a clinical T1 or T2 invasive ductal or lobular breast carcinoma, regardless of estrogen/progesterone/human epidermal growth factor receptor 2 (HER2) receptor status.
• Participants with clinical (on palpation) N0 and up to two suspicious lymph nodes on axillary ultrasound.
• Participant with biopsy-proven positive axillary disease made by core needle biopsy or fine-needle aspiration.
• Participants must have an Eastern Cooperative Oncology Group (ECOG) Scale of Performance Status less than 2.
• Participants must understand, accept, and have signed the approved consent form.

Exclusion Criteria:

• Participant with previous ipsilateral axillary surgery, including sentinel lymph node biopsy.
• Participants with distant metastases.
• Participants that have had previous radiotherapy to the axillary nodes.
• Participants who received neoadjuvant therapy.
• If the injection of blue dye is planned, patients with hypersensitivity or allergy to isosulfan blue, patent blue, methylene blue or radiocolloid dye.
• Participants who are unable to provide informed consent.