Prior to surgery, if the lymph nodes appear radiologically to be unaffected, they are sampled at the time of the surgery to remove the cancerous lesion. This is done by a radioactive isotope being injected into the affected breast, usually a few hours prior to surgery. Due to the way the breast tissue drains into the lymphatic vessels, the isotope will move through to the nearest lymph node to the cancer. This is known as the sentinel node. Blue dye is usually injected as a fail-safe measure. During surgery a small radiation monitor will be used to pinpoint the sentinel node, which is removed, along with a few surrounding lymph nodes, so that they can be properly checked under a microscope.
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