Terminal ducts connect the acini to the mammary ducts. The diagram below shows these anatomical features. The breast gets its blood supply from two main sources. The second is the lateral thoracic artery which is a branch of the axillary artery. This artery reaches the breast from under the arm up in the armpit.
Further blood gets to the breast from the acromiothoracic artery and the intercostal arteries.
The blood supply of the breast is critically important when trying to understand breast cancer and how it spreads. As a general rule anywhere in the body, cancer may spread by one of three means. In the case of the breast, the most common method of cancer spread is via the lymphatics and by direct invasion, but haematogenous spread also occurs. Another general rule in the body is that lymph vessels draining an organ, run alongside the arteries that supply blood to that organ. These are therefore the most common sites for lymph node metastases in breast cancer and are important when the stage and prognosis of the disease are being determined.