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In the current era, many patients present with a small primary breast cancer detected by mammography or other screening procedures. In recent decades, the median size of nodal metastases has decreased, paralleling the decrease in primary tumor size. The median size of nodal metastases is now approximately 6 mm,1 and 70% to 80% of patients have negative nodes after surgical and pathologic nodal staging. A systematic approach to the evaluation of lymph nodes is needed today to reliably identify metastatic carcinoma.

Sentinel lymph node (SLN) biopsy has led to the use of more sensitive pathologic techniques to reliably detect small metastases and reduce the risk of false-negative results. The nature of SLNs as first-draining lymph nodes, combined with the use of multilevel sections and cytokeratin immunohistochemistry, has significantly increased the number of patients with nodal micrometastases or isolated tumor cells2 and intensified the debate over the therapeutic benefit of axillary dissection and the clinical impact of minimal metastases on patient prognosis and choices for adjuvant therapies. Clinicians, including pathologists, need to understand that minimal nodal disease, when present, should be considered in the context of the primary tumor characteristics and the patient's clinical status. A multidisciplinary breast conference discussion helps to optimize individual patient care recommendations.

SLN biopsy performed by an experienced surgeon provides prognostic and staging information equivalent to that provided by axillary dissection. Validation studies, with comprehensive pathologic analysis of both SLNs and non-SLNs, have confirmed the accuracy and safety of SLN biopsy. 2-4 The accuracy of SLN biopsy compared with complete level I and II axillary dissection is greater than 95% at major centers.5 Axillary recurrence rates for patients with negative SLN biopsy followed by adjuvant therapies appear similar to recurrence rates for patients who have had complete axillary dissection.6

Nonsurgical alternative approaches to axillary staging have recently focused on ultrasound evaluation to determine whether SLN biopsy is indicated.7,8 Patients with a large primary tumor9,10 or suspicious axillary clinical examination may benefit from preoperative axillary ultrasound with fine-needle aspiration cytology or core biopsy of suspicious nodes (Chapter 24). Patients with a positive needle biopsy result can proceed to complete axillary dissection, whereas those with a negative or nondiagnostic result undergo SLN biopsy. Studies with fine-needle aspiration cytology have demonstrated a high level of accuracy for ultrasound-detected macrometastases, with a reduction of SLN procedures by 10% to 15% and resultant cost savings.9 Pathologists should be careful to avoid a false-positive result, which has been reported rarely.

Primary tumor typing with phenotypic and molecular genotypic assays, under investigation today,11 may help in the future to determine which patients benefit from SLN biopsy and complete axillary node dissection (CLND).

Optimal patient care derives from a well-functioning surgeon–pathologist team. Sentinel nodes should be submitted to pathology preferably as single nodes dissected free of adipose tissue and with a description ...

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