Axillary lymph nodes are described according to their position relative to the pectoralis minor muscle:
Rotter nodes are located between the pectoralis major and minor muscles and are considered at level II. Also known as interpectoral lymph nodes.
Breast cancer commonly infiltrates lymph nodes from level I to level II, to level III.
When the spread does not follow that pattern, this is called discontinuous or skip metastases. An uncommon finding.