There are three levels of axillary lymph nodes (the nodes in the underarm or “axilla” area):
Level I is the bottom level, below the lower edge of the pectoralis minor muscle.
Level II is lying underneath the pectoralis minor muscle.
Level III is above the pectoralis minor muscle.
A traditional axillary lymph node dissection usually removes nodes in levels I and II. For women with invasive breast cancer, this procedure accompanies a mastectomy. It may be done at the same time as, or after, a lumpectomy (through a separate incision).