![]() Dispersed pattern of lymph node metastasis can be difficult to categorize.Cases with isolated tumor cells only in lymph nodes are classified as pN0(i+).Size of the metastasis, not the size of the node, is used for the criterion for the N category.Tumor nodule with a smooth contour in a regional node area is classified as a positive node.Direct extension of primary tumor into a regional node is classified as node positive.Size of the metastatic focus is measured from the largest contiguous cluster of tumor cells.Metastasis to nonsentinel lymph nodes can occur if the true SLN is completely replaced by tumor (and therefore is not detected by radioactive tracer or dye), if there is unusual lymphatic drainage or if there is failure of the technique to identify the node.In most cases, if metastases are present, the SLN will be involved in rare cases, only nonsentinel nodes contain metastases.Atypical cases on FS are usually negative on permanent sections ( Mod Pathol 2005 18:58).FNR of intraoperative frozen section post neoadjuvant chemotherapy was 5.4% in a single institution study of 711 cases ( Am J Surg Pathol 2019 43:1377).SLN FS may be safely omitted in patients who meet ACOSOG Z11 criteria ( Clin Breast Cancer 2018 18:276, J Clin Pathol 2016 146:57).Frozen section (FS) had an overall mean sensitivity of 73% (macrometastasis: 94% micrometastasis 40%) and mean specificity of 100% (metaanalysis of 47 studies, Cancer 2011 117:250).Intraoperative frozen section or imprint cytology may be performed on the SLN to determine need for axillary lymph node dissection ( World J Surg Oncol 2008 6:69, Eur J Surg Oncol 2009 35:16).Axillary SLN are identified by the surgeon by determining uptake of radioisotope technetium 99 sulfur colloid, methylene blue dye or both.Current NCCN guidelines recommend strongly considering radiation therapy.Role of nodal radiation therapy in patients with 1 - 3 positive lymph nodes is unclear, though there is modest increase in disease free survival ( JAMA Oncol 2016 2:991).ER+ / HER2- patients with limited involvement of axillary lymph nodes might be spared adjuvant chemotherapy if the tumor biology is favorable ( Ann Oncol 2018 29:2153).Per current NCCN guidelines, clinically node negative patients with only micrometastasis or with macrometastasis meeting ACOSOG Z11 criteria (T1 / T2 tumor, ≤ 2 positive nodes, breast conserving surgery, whole breast RT planned, no preoperative chemotherapy) may be spared ALND.Number of involved lymph nodes and size of deposit (micro / macrometastasis) are important for clinical decision making ( Ann Oncol 2018 29:2153).Notable exception per Choosing Wisely Society of Surgical Oncology recommendations: don't routinely use SLNB in clinically node negative women ≥ 70 years of age with early stage hormone receptor positive, HER2 negative invasive breast cancer.SLN biopsy (versus ALND) is standard of care in staging clinically node negative T1 / T2 tumors.Tumor is more likely at the inflow junction of afferent lymphatic vessels ( Am J Surg Pathol 2003 27:385).Medially located tumors are more likely to drain to internal mammary nodes (medial 28% lateral 15%) ( Am J Clin Pathol 2018 150:4).If metastases are present in these nodes, there are specific AJCC N categories.Internal mammary nodes, supraclavicular nodes and infraclavicular nodes are rarely removed for breast cancer staging.Intramammary nodes are most commonly present in the upper outer quadrant and are included with axillary nodes in AJCC N classification.Apical axilla or infraclavicular nodes: medial to the medial margin of the pectoralis minor muscle and inferior to the clavicle.Mid axilla: between the medial and lateral borders of the pectoralis minor muscle, plus the interpectoral (Rotter) lymph nodes.Low axilla: lateral to the lateral border of the pectoralis minor muscle.Axillary lymph nodes are divided into 3 levels:.Perforating system: traverses pectoralis muscles and drains into internal mammary node.Deep system: breast to axilla, anastomoses with perforating system.Superficial system: superficial breast and skin to axilla, independent.Breast lymphatic drainage ( Am J Clin Pathol 2018 150:4):. ![]()
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