The lymphatic and venous drainages of the breast are of great importance in the spread of carcinoma.
About three quarters of the lymphatic drainage is to the axillary nodes:
(1) Lymphatics pass around the edge of the pectoralis major and reach the pectoral group of axillary nodes;
(2) routes through or between the pectoral muscles may lead directly to the apical nodes of the axilla;
(3) lymphatics follow the blood vessels through the pectoralis major and enter the parasternal (internal thoracic) nodes;
(4) connections may lead across the median plane and hence to the contralateral breast;
(5) lymphatics may reach the sheath of the rectus abdominis and the subperitoneal and subhepatic plexuses.
It should be noted that free communication exists between nodes below and above the clavicle and between the axillary and cervical nodes.