The lymph nodes in your underarm area are called axillary lymph nodes. They play an important role in the diagnosis and treatment of breast cancer. You have lymph nodes throughout your body. When cancer cells reach the lymph nodes, the cancer can spread to other parts of your body more easily. By looking at some of these lymph nodes under a microscope (biopsy), your doctor can see if your breast cancer has spread to them.

A sentinel node biopsy is surgery that removes the first one or two lymph nodes that cancer would travel to from the breast. An axillary lymph node dissection is surgery that removes usually 10 to 20 nodes.