Background: Most patients with a positive sentinel lymph node (SN) have no further metastases in the axillary lymph nodes and may therefore not benefit from axillary lymph node dissection. In patients with melanoma, evaluation of the centripetal depth of tumor invasion in the SN, also known as the S classification of SN, and microanatomic localization of SN metastases were shown to predict non-SN involvement. This phenomenon has been less extensively studied in breast cancer. We sought to validate the S classification and microanatomic location of SN metastases in breast cancer patients with regard to their predictive value for non-SN involvement and overall survival (OS).
Methods: A total of 236 patients with positive SN followed by axillary lymph node dissection were reevaluated according to the S classification and the microanatomic location of SN (subcapsular, parenchymal, combined subcapsular and parenchymal, multifocal, extensive) metastases to predict the likelihood of non-SN metastases and OS.
Results: S classification and the microanatomic location of SN metastases were significantly correlated with non-SN status (P < 0.001). Especially patients with a maximum depth of invasion ≤0.3 mm (stage I according to the S classification) and those with SN metastases only in subcapsular location had a low probability of further non-SN metastases (7.8 and 6.1%) and a good prognosis for OS.
Conclusions: S classification and microanatomic location of SN metastases predicts the likelihood of non-SN involvement. Especially patients with subcapsular or S stage I metastases have a low probability of non-SN metastases and a good prognosis for OS.