The lymph nodes reveal information about outlook and they help doctors determine the best types of treatment against the cancer. Your lymph nodes act as filters for your body's lymphatic drainage system. That's why the lymph nodes are likely to "catch" or filter out cancer cells that might be floating in the fluid that drains away from the cancerous area of the breast.

The surgeon will inject a blue dye and a radioactive substance (called a tracer) into the tumor or the skin over the tumor. The...