How can breast cancer spread?

Circulation: Most breast cancers begin in the milk-producing ducts and lobules. These cancer cells break out of these ducts and lobules and enter into the supporting tissue of the breast--that's why it's called invasive. Lymphatics and blood vessels are found within this supportive tissue. If the cancer cell enters these vessels, they can circulate throughout the body and take up residence in another organ.

3 ways: It spread through lymphatic organ ( lymph glands) , through blood circulation and direct invasion to the adjacent organ such as skin, chest wall etc.

Lymphatics: Breast cancer spreads through your lymphatic system.