Recent studies have shown that the false negative rate of sentinel lymph node (SLN) biopsy is less than 5% and SLN biopsy is accepted as a highly accurate method for evaluating axillary lymph node metastasis in breast cancer. Purpose of this study was to evaluate the relationship between the location of SLNs and external anatomical structures of axilla in order to help a proper skin incision.

Between July 2001 and May 2002, SLN biopsies were performed in 25 breast cancer patients. SLNs were detected by hand-held gamma probe after subareolar injections of 99m-Tc antimony sulfur colloid. The location of the SLNs was indicated in terms of distance and direction from the lateral border of pectoralis major muscle and the axillary hair line. Breast conserving surgery or mastectomy was performed with axillary dissection in all cases.

The location of tumors was the upper outer quadrant in 11 cases; the central portion in 4 cases; the upper inner quadrant in 4 cases; the lower inner quadrant in 3 cases; and the lower outer quadrant in 3 cases. Lymph nodemetastases were found in 5 cases of which SLNs were only metastatic nodes in 2 cases. The mean number of SLNs was 1.6. The false negative rate of SLN biopsy was 4.0% (1/25), giving a diagnostic accuracy of 96.0% (24/25). All the SLNs were located between the lateral border of pectoralis major muscle and the axillary hair line and the distance from the inferior tip of the hair line was as follows: 2 cases within 0.5 cm; 3 cases between 0.6 cm and 1 cm; 14 cases between 1.1 cm and 1.5 cm; 2 cases between 1.6 cm and 2.0 cm; 3 cases between 2.1 cm and 2.5 cm; 1 case between 2.6 cm and 3.0 cm. All the SLNs were located within a 3 cm diameter circle between the axillary hair line and the lateral border of pectoralis major muscle.

The SLNs in breast cancer are located in a small area between the lateral border of pectoralis major muscle and the axillary hair line.