Axillary lymph nodes
About 75% of the lymph from the breast goes to the axillary lymph nodes via the pectoral lymph nodes. This is the most important place to check for metastasis of the cancer cells! The lymph from the axillary nodes eventually drains into the subclavian lymph trunk.
Most of the rest of the lymph drains into the parasternal lymph nodes, while a small amount drains to the abdominal wall and the opposite breast. The anterior mediastinum is not an important place for lymphatic drainage from the breast.