Sentinel lymph node mapping and examination

SLNs were detected by lymphoscintigraphy with technetium-99m sulfur-colloid diluted in normal saline solution or indigo carmine blue dye. Blue dye was performed when lymphoscintigraphy was not available or when SLN mapping had failed. Radioactive isotope or blue dye was injected at a subareolar or peritumoral site. Lymph nodes registering a 10% or higher count than the highest ex vivo count via gamma probe were regarded as the SLNs.

SLNs analysis were initially performed by frozen or permanent section. Lymph nodes for frozen section were sliced into several blocks at 2-mm perpendicular intervals along the long axis of lymph node. The 80-µm blocks with a minimum of 2 levels were embedded at −20℃, and samples were taken with a microtome setting of 4 µm. Analysis of frozen slides was performed by a pathologist specialized in breast pathology. We fixed each block of remaining tissue, taken with a microtome setting of 4 µm, in 10% formalin and embedded these tissues in paraffin. Serial sections were stained with H&E for pathological analysis. The other side of each node was stained for immunohistochemistry.