An important consideration for sufferers of breast cancer as malignant cells tend to spread via the lymphatics.
Most of the drainage from the breast goes to axillary lymph nodes. Some goes to subclavian nodes via interpectoral nodes (Rotter's nodes). Strangely enough, a little goes to the contralateral breast. Finally, a little goes to subdiaphragmatic lymph nodes.
When performing a mastectomy for breast cancer, nodal clearance is often necessary. Miss an important node and cancer is likely to recur. Take out too many nodes and other problems like lymphodema might occur.
A new surgical method called intraoperative sentinel lymph node biopsy is being trialled for effectiveness and safety. If successful, future mastectomy operations will result in far fewer incidences of lymphodema simply because fewer lymph nodes have to be removed.