This single-center randomized controlled trial evaluates whether detecting the first lymph node at the axillary entrance with ultrasound guidance, followed by a targeted axillary incision over the pencil-marked projection, improves sentinel lymph node identification compared to the conventional axillary hairline landmark. The study hypothesizes that this technique enables a smaller incision, minimizes tissue dissection, and reduces operative time.

Axillary lymph node status is a key prognostic factor in breast cancer treatment planning. Accurate axillary staging is essential for optimal management. Sentinel lymph node biopsy (SLNB) provides reliable nodal assessment and is associated with lower morbidity relative to axillary dissection. The sentinel lymph node is the initial recipient of lymphatic drainage from the primary tumor, and breast lymphatics typically drain into at least one sentinel node.

The majority of sentinel nodes are located in level I, particularly within the anterior axillary (pectoral) lymph nodes. These nodes are positioned at the inferolateral border of the pectoralis minor muscle, adjacent to the lateral thoracic vessels, and are typically in contact with the axillary tail of the breast.

The standard axillary incision for SLNB is performed parallel to the Langer line, below the axillary hairline. Blue-stained lymph nodes are identified and excised by following the blue-stained lymphatic channels.

The anterior axillary (pectoral) lymph node can be identified by placing the ultrasound transducer on the flattened lateral breast and axillary tail after appropriate patient positioning. Ultrasound guidance during an axillary incision at the projection of this lymph node allows direct access to the blue-stained sentinel lymph node. This approach reduces the extent of dissection and the need for channel tracking compared to the standard technique, resulting in a smaller incision, less tissue dissection, and shorter operative time.

This study evaluates whether ultrasound-guided projection of the first lymph node at the axillary entry during an axillary incision, followed by tracing the blue-stained lymphatic channel and identifying adjacent lymph nodes, reduces operative time and morbidity by minimizing dissection compared to the standard axillary hairline landmark approach.

Inclusion Criteria:

• * Patients with clinical stage T1-T3 disease (tumor ≤5 cm), pN0-pN1 (one to three regional lymph nodes with micrometastases or metastases), and M0 (no distant metastasis) are eligible. Post-neoadjuvant yT1-T3, yN0-yN1, and M0 status are also eligible. All patients are undergoing axillary staging.
• Clinically negative axilla
• Written informed consent must be obtained prior to inclusio

Exclusion Criteria:

• Younger than 18 years
• Previous breast malignancy
• Pregnancy
• Pre-operative diagnosis of axillary lymph node metastases
• The presence of multiple clinically involved or suspicious lymph nodes
• Unable or unwilling to provide informed consent.

Patients scheduled for sentinel lymph node biopsy due to breast cancer at Antalya Training and Research Hospital.